Bicycle Turn Signal

[janagyjr]

I'm getting ready to start purchasing the materials for a 12-LED bicycle turn signal and I was wondering if anyone could give me some pointers or tips on stuff I haven't already considered?

The link to the project files can be found here:
http://www.joseph-a-nagy-jr.us/projects/personal/index.html

Has anyone else engaged in a similar project? Something I'm not sure how to do is weatherproofing everything while still making it so I can go back in and replace components as needed.

 

[webmasterpdx]

I didn't have time to download the whole project. Would have been easier if there was a diagram or something on that other homepage. However, such a project is so easy in the first place. Here is how I'd do it.

1. 2 buttons on the handlebars either a rocker switch to go right/left or one botton on each side of the handlebars. I'd use a cheap wireless adapter (you can get them for under $10....since it's just for yourself, you don't have to worry about the FCC). Then you don't have to run wires....which will make it more weather proof. Placing the rocker switch in the right place can make it weather proof, and having a cap you can remove or open before riding can protect it outdoors. Alternatively if using buttons, just place the buttons under heated on plastic so it shrinks onto the buttons...or use a touch sensitive arrangement.

2. The receiver end on the back of the bike only needs a simple PIC or similar low cost microcontroller. I think it'd be more visible to just have 2 big arrow cutouts and place an LED behind each rather than a cylon effect (which is what I presume you are using). Making this part effectively waterproof is fairly simple (just seal it with a box with a latch, so it can be opened). There is the issue of making the thing visible during the day. Having a simple arrow on a stick with a servo motor might be better and it pops down to the right or left. This is instead of a light. Weatherproofing is more difficult for this approach.

3. Use a single AAA for the button and AA for the lights. Make sure you use an efficient joule thief circuit so you get every drop from your battery....that'll double your battery life.
You could alternatively use a supercap and recharge it from a bike dynamo whenever it runs low.

4. Consider also using it as brake lights too.

5. Remember, if it's too fancy looking, someone may steal it....so someway to disguise it as nothing when you lock your bike.

I did something similar for nighttime roller blades a few years ago. In that case, we wanted brake lights and we were also trying something unique as a speedometer. We had 2 ideas that might interest you if you like bike electronics. The first was to use an optical mouse chip to determine velocity, looking at the shaft of the bike wheel. The second was to use audio of the ground and use autocorrelation on the assumption that whatever noise the front wheel makes, the back wheel will make similar but offset in time (due to the wheels going over the same bumps on the ground). From the resulting curve and the distance between the wheels you can calculate the velocity. This is more applicable to roller blades than bikes, but it might work. You have to filter out ambient sounds and with autocorrelation, there are always erroneous results you'll have to smartly filter out.

Good Luck
-Donald

 

[janagyjr]

I didn't have time to download the whole project. Would have been easier if there was a diagram or something on that other homepage. However, such a project is so easy in the first place. Here is how I'd do it.

I thought about that, but it wouldn't look too good on the two column layout I've got going there. It's under half a MB so it shouldn't take too long to download.

1. 2 buttons on the handlebars either a rocker switch to go right/left or one botton on each side of the handlebars. I'd use a cheap wireless adapter (you can get them for under $10....since it's just for yourself, you don't have to worry about the FCC). Then you don't have to run wires....which will make it more weather proof. Placing the rocker switch in the right place can make it weather proof, and having a cap you can remove or open before riding can protect it outdoors. Alternatively if using buttons, just place the buttons under heated on plastic so it shrinks onto the buttons...or use a touch sensitive arrangement.

I was thinking three position wired rocker switch but wireless will work just as well. Just hope the hobby box I'm getting will have room for the receiver.

2. The receiver end on the back of the bike only needs a simple PIC or similar low cost microcontroller. I think it'd be more visible to just have 2 big arrow cutouts and place an LED behind each rather than a cylon effect (which is what I presume you are using). Making this part effectively waterproof is fairly simple (just seal it with a box with a latch, so it can be opened). There is the issue of making the thing visible during the day. Having a simple arrow on a stick with a servo motor might be better and it pops down to the right or left. This is instead of a light. Weatherproofing is more difficult for this approach.

Do I actually need a PIC or microcontroller for putting the receiver output to the chip? All I'm turning on is a 555 timer to control the blinking. The switch itself is actually in the middle of the circuit (between the pin 3 output and the LEDs) with a simple npn transistor (and accompanying resistor on the base) right before the switch.

3. Use a single AAA for the button and AA for the lights. Make sure you use an efficient joule thief circuit so you get every drop from your battery....that'll double your battery life.
You could alternatively use a supercap and recharge it from a bike dynamo whenever it runs low.

Do you think one AA will power 6 LEDs (6 per side; two parallel banks of three)?

I've actually got access to a bike dynamo (from my dad's old bike brake light and headlight system) so that's something to consider.

4. Consider also using it as brake lights too.

I have been thinking about it, though it seems it would require a multi-position chip and something bigger than a 2N3904 transistor and a 555 timer. I don't want to saturate the timer or the transistor.

5. Remember, if it's too fancy looking, someone may steal it....so someway to disguise it as nothing when you lock your bike.

This is probably going to be pretty ugly.

I did something similar for nighttime roller blades a few years ago. In that case, we wanted brake lights and we were also trying something unique as a speedometer. We had 2 ideas that might interest you if you like bike electronics. The first was to use an

Share away.

optical mouse chip to determine velocity, looking at the shaft of the bike wheel.

I actually took one apart the other day in a vain attempt at fixing the thing. The wire where it goes into the mouse was giving me an on/off condition though I couldn't find an actual physical break when I snipped out that part, going to splice the wire back together and heat shrink everything up, if that don't work, though, it's parts.

The second was to use audio of the ground and use autocorrelation on the assumption that whatever noise the front wheel makes, the back wheel will make similar but offset in time (due to the wheels going over the same bumps on the ground). From the resulting curve and the distance between the wheels you can calculate the velocity. This is more applicable to roller blades than bikes, but it might work. You have to filter out ambient sounds and with autocorrelation, there are always erroneous results you'll have to smartly filter out.

Good Luck
-Donald

Thanks, definitely a lot to consider. My only concern is it becomes like that junky multi-function light that claims to be a turn signal that I bought from Wal*Mart (Bell or Schwinn brand) and the fact I can't find anything like what my dad has on his bike (which is the frustration that birthed this idea in the first place).

 

[webmasterpdx]

PIC vs 555

A PIC is about the same size and probably not much more expensive than a 555 timer. It has an internal clock. I think the one I mentioned has an 8MHz internal clock. It has 6 configurable i/o pins, 2 internal timers (fully programmable). 4 lines can be configured as A/D (but there is only one A/D unit, as it can be used for different pins at different times). You would output the PWM using a timer. However, you'd need more pins to drive 6 LEDs....just get a PIC that is 50 cents more.
As for voltage, look up joule thief. This is a circuit to learn about while you are young....which I suspect. It can change your voltage and give you every last drop of power from your battery. You might be able to use an AA for that, but a PP3/9V might be better for what you want.
Note that the original joule thief isn't very efficient. There are lots of examples of more efficient ones with minor modifications. Great little circuit.

If you don't want to learn programming, you can do all this with the 555, but you won't be able to use a transceiver (you'll need some smarts to receive data). The joule thief will work with either circuit....I'm surprised this circuit isn't used more. IMO it should be in every LED flashlight.

 

[janagyjr]

A PIC is about the same size and probably not much more expensive than a 555 timer. It has an internal clock. I think the one I mentioned has an 8MHz internal clock. It has 6 configurable i/o pins, 2 internal timers (fully programmable). 4 lines can be configured as A/D (but there is only one A/D unit, as it can be used for different pins at different times). You would output the PWM using a timer. However, you'd need more pins to drive 6 LEDs....just get a PIC that is 50 cents more.

Even when they are hooked up in parallel (3 per branch) with a transistor doing the actual switching?

As for voltage, look up joule thief. This is a circuit to learn about while you are young....which I suspect. It can change your voltage and give you every last drop of

I am looking it up now, though you better watch your assumptions. (;

power from your battery. You might be able to use an AA for that, but a PP3/9V might be better for what you want.
Note that the original joule thief isn't very efficient. There are lots of examples of more efficient ones with minor modifications. Great little circuit.

If you don't want to learn programming, you can do all this with the 555, but you won't be

I have access to a programmer board and software to program PICs (from mikroelectronika).

able to use a transceiver (you'll need some smarts to receive data). The joule thief will work with either circuit....I'm surprised this circuit isn't used more. IMO it should be in every LED flashlight.

Like I said, I'm not against changing my design. 555 timer was the first thing I thought of as I just learned about them as an elective to my main course of study (I'm at a trade school studying to be an electrician, the same class is used to teach electronics technology and I can pick up a certificate in the other course (for me electronics) by studying it as an elective). The electronics portion does teach PIC/microcontroller programming in addition to the normal parts of the class so that's not an issue.

Attached you'll find a PDF with my current circuit design. If I decide to go with a PIC, I'll probably ignore this thread for a little while (around 3 months).

 

[(*steve*)]

One think to keep in mind is that a "joule thief" is simply a method of getting a usable higher voltage from a low voltage source. It doesn't mean that they are efficient, nor particularly recommended for a high current application.

You have 4 strings of three LEDs (only 2 turned on at any one time) so you will require 40mA for the LEDs at nominally 9V.

With 100% efficiency, that would be 240mA from a 1.5V battery. Realistically speaking, you might be lucky to get 50% efficiency from a "Joule Thief", so you would have a current drain of around half an amp from the AA cell.

OK, you can get the average by factoring the duty cycle (half for 50%) but unless you use a very small duty cycle, the average current from a 1.5V battery will still be quite high.

My personal suggestion is to go for a higher voltage supply. See if you can squeeze 6 AA cells in there (or 6 AAA cells even)

In daylight, I would suggest you won't see the LEDs.

OK, now for some other issues with your circuit:

1) The Diode D13, presumably to protect the circuit from reverse polarity is the wrong way around. Given the nature of the power source, and the desire for efficiency, I'd suggest moving it so that it is reverse biased across the supply rails. That will short the battery if it is inserted backwards. Alternatively, you could wire up the common side of the LEDs to the other side of the diode. This has significant other benefits.

2) The supply to the 555 is not isolated from that tot he LEDs and battery impedance may cause the voltage to sag. Whilst the 555 is pretty tolerant, it could cause triggering problems. I would advise using a diode to isolate the LED power from the 555 power (as noted above) and place a (say) 100uF capacitor across the power pins of the 555. This will reduce the power supply fluctuations seen by the 555.

3) your use of a small (0.1uF) capacitor and high value (6 and 8 Mohm) resistors will be problematic, Perhaps you chose them because they would result in lower current draw? The issue is that the input currents of the 555 will liekly mean that the operation will be unreliable. In addition, humidity (something hard to exclude) will have the effect of changing the resistance. I would tend to suggest resistors a factor of 100 lower in resistance (62 and 82 k) and a larger capacitor (10uF?) If you have breadboarded this and decided on those resistors by trial and error, you may fend you need a significantly smaller capacitor.

4) the small base resistor on the transistor will mean an excessive base current. You will be providing 27mA of base current to switch a load of 40mA. Even the lowest gain power transistors switching large currents have a gain of more than 1.5! Typical small signal transistors will have a current gain of more than 100 at these currents, so you need perhaps 1/100th of the base current. a 22k base resistor may be more appropriate. Also consider that the 555 can drive a load at up to 200mA. The transistor may not be required (but having it allows you to better isolate the 555 from fluctuations in supply voltage). Note that the transistor may requrie a little more base drive than I have suggested to be fully saturated, but datasheets will tell you what you need to know.

5) It would be nice to know what colour LEDs you're planning to use. Your circuit seems to be based on red LEDs and a 1V drop across the transistor perhaps? Your LED current may vary wildly from 20mA if they are different colour LEDs with different Vf -- what are you using and what have you assumed about them?

6) the switch arrangement is OK, but you might want to think of another arrangement that allows you to use simple SPST switches. For example, take my advice about reversing the diode, and moving the LED common signal to the other side of the diode, then... Remove the switch connected between the transistor and the diodes (so they're always connected. Now split the LED common so that you have a switch and a diode for each set of LEDs. Either button press will provide power and light one string of LEDs. The diode now does 3 things, it isolates the 555 power, it prevents current flowing backward to light the other string of LEDs, and it still protects against reverse polarity.

Apart from that, the basic concept is fine, and I see no real advantage in moving to a PIC (although that would work fine too)

 

[webmasterpdx]

Much Better

Ah, this is different than what I thought you had in mind. This is much simpler.
I wouldn't bother trying to complicate it (unless you want it to get fancy) by using a PIC. This circuit can be put on a piece of protoboard, so you don't even need a PCB (unless you are buying it as a kit).

I think the diode is wrong way around by the power supply.

The joule thief keeps the voltage up, so it's more used for cases where you use a AA battery to make the battery last longer and keep the voltage high enough to drive an LED longer (so the battery lasts longer). In this case, since you are using a 9V battery and the circuit is so simple, I wouldn't complicate it by adding a joule thief. BTW, when I say joule thief, as I said earlier, never use the "standard" joule thief circuit as it is very inefficient, but use one of the efficient design mods (there are plenty on the web that only add an extra transistor or something to give you 90% efficiency). But in this case, I wouldn't bother with it.

I would breadboard it first and play with the resistor to the transistor. You might find it a bit low and it could make the transistor get a bit hot. I think your circuit might work fine with a 10K resistor. Remember, Ic = Hfe Ib. Hfe is a characteristic for the transistor (which you can find on the web in it's datasheet). Depending on who's 555 you are using the current from the pin could be a couple of hundred mA (you'd need to look that up too), and based on that, you should be able to calculate the resistor value to give you the Ic you want. Or you can use a bigger resistor over and over on a breadboard until it works the way you want it with the biggest resistor possible.

This will be a nice design for at night, but like I said before, I'm unsure if anyone is going to see it during the day.

You might be adised to stick to the arm signals and put reflective armbands on your arms (2 on each arm...upper and lower....would be best). You might also see what the law says about this. You might be required to use arm signals anyways, even if you have this device on your bike.

As for your daylight problem. It might work with superbright LEDs. I think most of these are made for flashlights though. What you could do is put a white superbright one behind a red reflector (you can get these anyplace), just like a car's. Note that these LEDs typically require constant current circuitry. There is a good tutorial on LEDs on this page that talk about these.

Good Luck.
You know, it's just a fun circuit, so build it anyways for the fun of it. If you are studying electronics, you'll just get more experience....which is a good thing. It won't take you more than an hour to breadboard it and play around with it. If you don't have a breadboard, I'd recommend one. They are fun and can save you all kinds of mistakes.

-Donald

 

[janagyjr]

One think to keep in mind is that a "joule thief" is simply a method of getting a usable higher voltage from a low voltage source. It doesn't mean that they are efficient, nor particularly recommended for a high current application.

Alright.

You have 4 strings of three LEDs (only 2 turned on at any one time) so you will require 40mA for the LEDs at nominally 9V.

With 100% efficiency, that would be 240mA from a 1.5V battery. Realistically speaking, you might be lucky to get 50% efficiency from a "Joule Thief", so you would have a current drain of around half an amp from the AA cell.

That's quite a bit.

OK, you can get the average by factoring the duty cycle (half for 50%) but unless you use a very small duty cycle, the average current from a 1.5V battery will still be quite high.

My personal suggestion is to go for a higher voltage supply. See if you can squeeze 6 AA cells in there (or 6 AAA cells even)

Wired in series, I assume? That's looking at the same as one 9V. Any particular reason for using multiple batteries over one?

In daylight, I would suggest you won't see the LEDs.

The LEDs are rated at 1200mcd.

http://www.superbrightleds.com/cgi-...on=DispPage&Page2Disp=/specs/R12120_specs.htm

OK, now for some other issues with your circuit:

1) The Diode D13, presumably to protect the circuit from reverse polarity is the wrong way around. Given the nature of the power source, and the desire for efficiency, I'd suggest moving it so that it is reverse biased across the supply rails. That will short the battery if it is inserted backwards. Alternatively, you could wire up the common side of the LEDs to the other side of the diode. This has significant other benefits.

I thought it looked wrong. I still have a bit to learn about reading schematics with regards to diodes.

2) The supply to the 555 is not isolated from that tot he LEDs and battery impedance may cause the voltage to sag. Whilst the 555 is pretty tolerant, it could cause triggering problems. I would advise using a diode to isolate the LED power from the 555 power (as noted above) and place a (say) 100uF capacitor across the power pins of the 555. This will reduce the power supply fluctuations seen by the 555.

That was something I hadn't considered.

3) your use of a small (0.1uF) capacitor and high value (6 and 8 Mohm) resistors will be problematic, Perhaps you chose them because they would result in lower current draw? The issue is that the input currents of the 555 will liekly mean that the operation will be unreliable. In addition, humidity (something hard to exclude) will have the effect of changing the resistance. I would tend to suggest resistors a factor of 100 lower in resistance (62 and 82 k) and a larger capacitor (10uF?) If you have breadboarded this and decided on those resistors by trial and error, you may fend you need a significantly smaller capacitor.

I actually came up on those values for the RC timing circuit (R1, R2 and C1) using a small program called 555 timer. I shouldn't hit the "smallest" button so much, I think (it reduces the capacitor to the smallest value and adjust the resistors to maintain the output). Lowering the resistors and raising the capacitance as you suggested still gets me the on/off timing I think would be appropriate (I'm not sure what a standard blink rate is). Since I will be using this on a bicycle I will be riding on the road often, I'm trying to make this as visible as possible without using incandescents.

4) the small base resistor on the transistor will mean an excessive base current. You will be providing 27mA of base current to switch a load of 40mA. Even the lowest gain power transistors switching large currents have a gain of more than 1.5! Typical small signal transistors will have a current gain of more than 100 at these currents, so you need perhaps 1/100th of the base current. a 22k base resistor may be more appropriate. Also consider that the 555 can drive a load at up to 200mA. The transistor may not be required (but having it allows you to better isolate the 555 from fluctuations in supply voltage). Note that the transistor may requrie a little more base drive than I have suggested to be fully saturated, but datasheets will tell you what you need to know.

Assuming 9V on the output, you're talking about 406uA. If I'm going to need more than 30mA to drive each bank, I'm going to need way more than 406uA. A 45 ohm resistor at 9V will give me 200mA through the transistor if I want to saturate both the transistor and the 3904. I found a 40 LED timer project, but it isn't switched manually like mine is.

5) It would be nice to know what colour LEDs you're planning to use. Your circuit seems to be based on red LEDs and a 1V drop across the transistor perhaps? Your LED current may vary wildly from 20mA if they are different colour LEDs with different Vf -- what are you using and what have you assumed about them?

See above link, assumed 1.85V drop on each (measured; calculating for 2V as listed and designed).

6) the switch arrangement is OK, but you might want to think of another arrangement that allows you to use simple SPST switches. For example, take my advice about reversing the diode, and moving the LED common signal to the other side of the diode, then... Remove the switch connected between the transistor and the diodes (so they're always connected. Now split the LED common so that you have a switch and a diode for each set of LEDs. Either button press will provide power and light one string of LEDs. The diode now does 3 things, it isolates the 555 power, it prevents current flowing backward to light the other string of LEDs, and it still protects against reverse polarity.

Apart from that, the basic concept is fine, and I see no real advantage in moving to a PIC (although that would work fine too)

Thanks for all the tips, I hope I don't sound to argumentative or protective of my circuit. It's the first one I've actually designed outside of op amps (and that was nearly 10 years ago).

 

[janagyjr]

Ah, this is different than what I thought you had in mind. This is much simpler.

Anything too complicated and I wouldn't even be trying to attempt it right now.

I wouldn't bother trying to complicate it (unless you want it to get fancy) by using a PIC. This circuit can be put on a piece of protoboard, so you don't even need a PCB (unless you are buying it as a kit).

I am not buying a kit per-say, but I am getting a hobby box that has a protoboard that's a bit bigger than I need.

I think the diode is wrong way around by the power supply.

I believe you are right. As Steve pointed out. I'm fixing it now.

The joule thief keeps the voltage up, so it's more used for cases where you use a AA battery to make the battery last longer and keep the voltage high enough to drive an LED longer (so the battery lasts longer). In this case, since you are using a 9V battery and the circuit is so simple, I wouldn't complicate it by adding a joule thief. BTW, when I say joule thief, as I said earlier, never use the "standard" joule thief circuit as it is very inefficient, but use one of the efficient design mods (there are plenty on the web that only add an extra transistor or something to give you 90% efficiency). But in this case, I wouldn't bother with it.

I'm still going to make one, just make it a separate project (something fun to do).

I would breadboard it first and play with the resistor to the transistor. You might find it a bit low and it could make the transistor get a bit hot. I think your circuit might work fine with a 10K resistor. Remember, Ic = Hfe Ib. Hfe is a characteristic for the transistor (which you can find on the web in it's datasheet). Depending on who's 555 you are using the current from the pin could be a couple of hundred mA (you'd need to look that up too), and based on that, you should be able to calculate the resistor value to give you the Ic you want. Or you can use a bigger resistor over and over on a breadboard until it works the way you want it with the biggest resistor possible.

I won't know the who for the timer until I put in my order at Tayda Electronics.

This will be a nice design for at night, but like I said before, I'm unsure if anyone is going to see it during the day.

You might be adised to stick to the arm signals and put reflective armbands on your arms (2 on each arm...upper and lower....would be best). You might also see what the law says about this. You might be required to use arm signals anyways, even if you have this device on your bike.

I need a signal because my left arm doesn't completely straighten out (former pediatric cancer patient).

As for your daylight problem. It might work with superbright LEDs. I think most of these are made for flashlights though. What you could do is put a white superbright one behind a red reflector (you can get these anyplace), just like a car's. Note that these LEDs typically require constant current circuitry. There is a good tutorial on LEDs on this page that talk about these.

I'm only buying LEDs from super bright. They also have car taillight, parking light, and turn signal kits (as well as inside dome lights). I'm trying to talk my mom into converting over from incandescents.

Good Luck.
You know, it's just a fun circuit, so build it anyways for the fun of it. If you are studying electronics, you'll just get more experience....which is a good thing. It won't take you more than an hour to breadboard it and play around with it. If you don't have a breadboard, I'd recommend one. They are fun and can save you all kinds of mistakes.

-Donald

I have a bread board from my days at ITT Tech Institute (I was studying electronics engineering technology back in the late 90s). I love using it, I just don't have a lot of stuff at home to make it useful (no regulated power supply or oscilloscope).

Steve, I replied to you but the board ate my reply, I think. ):

 

[webmasterpdx]

Sounds like you have a bead on things....

Sorry about the arm. I have injured arms too from half my garage falling on me, so it just hurts to do anything much with my arms (both of them), so I can relate.

I think it's good that you are building the joule circuit as it is a good circuit to help understand analog electronics, and could prove useful to you at a later stage.

Radio shack sell cheap regulated power supplies with multiple plug types on the end for around $50...I'm sure you can get one on ebay for $10. Get the regulated one though, as unregulated is pretty useless. I got one there and it's noise is almost as good as my pro supply (I have one of those $500 supplies). It only has a couple of voltages though, but that is still pretty cool. Note that this is another project worth building.....an LM317 variable regulator based circuit for giving you any voltage you want.....is interesting to play around with it.
You can also use a 9V battery on a breadboard!!!!

I think you have a good handle on things. Good luck to you.
-Donald

 

[janagyjr]

Sorry about the arm. I have injured arms too from half my garage falling on me, so it just hurts to do anything much with my arms (both of them), so I can relate.

I think it's good that you are building the joule circuit as it is a good circuit to help understand analog electronics, and could prove useful to you at a later stage.

I've always been intrigued with how things work and only have recently (my stint at ITT not withstanding) been able to indulge in my inner gadget geek to this level.

Radio shack sell cheap regulated power supplies with multiple plug types on the end for around $50...I'm sure you can get one on ebay for $10. Get the regulated one though, as unregulated is pretty useless. I got one there and it's noise is almost as good as my pro supply (I have one of those $500 supplies). It only has a couple of voltages though, but that is still pretty cool. Note that this is another project worth building.....an LM317 variable regulator based circuit for giving you any voltage you want.....is interesting to play around with it.
You can also use a 9V battery on a breadboard!!!!

I think you have a good handle on things. Good luck to you.
-Donald

Yeah, I might actually have something that has just the connector and some leads that I can salvage it from. I love my breadboard, though.

 

[(*steve*)]

Wired in series, I assume? That's looking at the same as one 9V. Any particular reason for using multiple batteries over one?

Yes.

9V batteries (the small 216 style) are not capable of delivering 40mA for very long. Their life will be short. Added to this, they are relatively expensive considering you would want to purchase a really good one to give you a reasonable life. On the other hand, AA cells are cheap, and 40mA is not a large current to draw from them. Cheap ones will do fine.

Having said that, indicators are not turned on for too long.

The LEDs are rated at 1200mcd.

OK, perhaps "visible" was not the right word. Try "noticable". Imagine driving up behind a bike during the day. Will you be loking at some odd thing on the back of a bike to warn you that the rider intends to pull out in front of you? Would you notice his arm sticking out just a tad more?

I guess you have a pretty good excuse for not sticking your arm out though. Perhaps you should consider placing the LED arrangement on a vest (it will be closer to where drivers look) as well as wearing reflective arm bands (that will make your indication with whatever movement you have more visible at night). Or maybe consider moving to a place that drives on the left side of the road. That way your left arm will be less of an issue

At night, the LEDs will be far more visible -- However, the arrow shape would need to be clearly visible or (and preferably AND) be sufficiently off centre to make it obvious for someone with relatively poor eyesight to figure out what they mean and to make the direction obvious.

1200mCd is not very bright these days. However beware that the brightness is generally achieved by reducing the half angle. As soon as you are off axis, or diffuse the light, it is far less bright.

I thought it looked wrong. I still have a bit to learn about reading schematics with regards to diodes.

Heh, easy mistake to make. Probably easier to actually wire it up that way by mistake. Bit you should catch it pretty fast

Since I will be using this on a bicycle I will be riding on the road often, I'm trying to make this as visible as possible without using incandescents.

Fair enough.

Assuming 9V on the output, you're talking about 406uA.

Yep, that's about right, it should be enough. Remember that the transistor has a current gain that should be more than 100, so you should see a collector current of around 40mA or more.

If I'm going to need more than 30mA to drive each bank, I'm going to need way more than 406uA. A 45 ohm resistor at 9V will give me 200mA through the transistor if I want to saturate both the transistor and the 3904. I found a 40 LED timer project, but it isn't switched manually like mine is.

I think you misunderstand. The transistor needs only a small base current to switch a much larger collector current. The base resistor can (and should) be much larger to limit the base current to what is required. Otherwise, you will be wasting almost as much power in that base resistor as you are delivering to the LEDs. You could also consider a logic level mosfet as a switch, but a bipolar transistor is fine.

See above link, assumed 1.85V drop on each (measured; calculating for 2V as listed and designed).

You may find that your LED current is significantly higher than the 20mA you specify on the circuit diagram. That's not a huge issue, as it allows some margin for the transistor not being driven to saturation.

I would breadboard it first, and determine what the LED current actually is. It will vary depending on the characteristics of the transistor, you need to allow sufficient base current to turn it on, but not so much that you waste power, and not so little that the LEDs are dim.

Thanks for all the tips, I hope I don't sound to argumentative or protective of my circuit. It's the first one I've actually designed outside of op amps (and that was nearly 10 years ago).

No problems.

 

[(*steve*)]

OK, check out the datasheet for the 2N3904. Page 2 specified a minimum current gain of 60 for a collector curent of 50mA and a voltage drop of 1V.

I always think something like BC547 for applications like this. The graphs show it has a typical gain of 150 at 50mA collector current.

Both will work fine. 1mA of base current should come pretty close to saturating them (the 400uA would probably turn them on quite nicely too)

Those LEDs have a max continuous current of 30mA. I would aim for 20mA. With your current values, you should be OK.

edit: Those LEDs have a wide beam, and you can clearly get away with viewing them significantly off-axis.

 

[janagyjr]

Yeah, I downloaded the datasheet earlier, and what I learned there was in my reply that the board ate (it said I couldn't reply or some such, it refreshed to the thread to quickly for me to catch). So 22k ohm resistor on the base of the transistor, move the polarity protection diode (which I've already reversed in my diagram so it's correct) as suggested, and perhaps change up the switching (the switch is going to be the hardest, I think, to put in since it's going to be running from my handlebars and comes in the "middle" of this circuit, that's going to be fun to wire).

I'm glad I posted here, I would have blown a few components otherwise. Definitely incentive to over-buy my components (a ten-spot for 100 555 timers sounds quite nice to me).

This will probably be my last post for a few days until I get some stuff worked out and prototype this on my breadboard.

edit: Using AA or AAA batteries significantly changes my power options. I was hoping to put the batteries in the case with the lights while still making it small enough to put in the traditional place on the bike. This will require some more thought on my part.

edit: Those LEDs have a wide beam, and you can clearly get away with viewing them significantly off-axis.

That's why I chose them, though I wish they were brighter.

 

[(*steve*)]

Here's what I was getting at with respect to using spst switches and diodes.

Obviously most of the 555 stuff is omitted for clarity (and laziness)

 

[janagyjr]

Updated Circuit

Attached is the updated circuit, let me know what you guys think.

edit:
Hopefully I can begin work on breadboarding this circuit over the Christmas holiday, I'll be posting pictures of progress (and perhaps some video to my YouTube channel) as I work on it. I'm getting ready to post some pictures of an old video descrambler I scrounged for parts (got 99% of the capacitors off, a handful of diodes, and a resistor (2.2MΩ)). If there is somewhere on this forum you guys would like me to post them, let me know.

 

[webmasterpdx]

That switch doesn't look right. I think you wanted to have a rocker switch.
If you do this:

         +----------------------------------------------------
----+----+                                                    rest of circuit
          +---------------------------------------------------

You have a 3 pole rocker switch. In the top position, it turns on the right batch of LEDs
In the bottom position, it turns on the left batch of LEDs.
In the middle position, the system is turned off.

This way, it also acts as your power switch.

Later
-Donald

 

[janagyjr]

The rocker switch could be placed back in, but it was suggested two spst switches (one for each hand) which would perform the same function. Since even a decent three-position rocker switch costs nearly $7, if two spst switches are cheaper, I'm going to go with that (Tayda has 22AWG wire for $0.10 a foot so wire cost isn't an issue) instead. Either way, I'm going to have to seal the switches against water with some sort of boot.

 

[webmasterpdx]

wire

When running wire back through the bike.....get an old appliance that someone wants to throw away and see if it has any old cable. Often you'll get a wire holding multiple wires inside it. That way, you are only running a single cable back (this is less fault prone, easier to implement and more weather proof).

Have fun.
-D

 

[(*steve*)]

Although it may be counter-intuitive, I'd put the left indicator on the right handlebar, and the right indicator on the left handlebar. That way you can do both arm signals and lights (rather than having one preclude the other).