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Help how to build a dc voltage interrupter to control power on and off time. PWN not sutable.

lostbit01

Sep 7, 2023
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Hello and good day out there and thank you for peeking at my first post here.

So I am making dew heaters for my telescopes, getting hard and expensive to buy
right now.
So I am using 12 volts +dc the source is about 2 amps and the load is 55 ohms.
I need a way to have the power on for maybe 40 seconds and turn off for
a range of 10,20,30 seconds. I tried using RC circuit to slowly charge and turn off a transistor.
no luck with that. I looked at PNP transistors but I would need a -DC supply.
I can do this with an Arduino but I think simple is better and I have plenty of transistors and
caps, Oh I will be making different ones for different setups. What I use now is an NPN power transistor
but it just does not give me the off state I want.
Anyway thank you for reading
Harry
 

danadak

Feb 19, 2021
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If you use a Nano or Uno board timing is very accurate, as they both have xtal oscillator
on them.

Easy way is use mBlock to do the code. Here I have 3 inputs each with a button, a pullup,
and one output to drive NPN or MOSFET to control heater power. mBlock takes block
configuration and converts to Arduino code, then uses Arduino programmer to program board.

You could use 8 pin DIP ATTINY85 to do the job. Use UNO or Nano to program it.

Basically mBlock detects a key is down, then loops until its released, then invokes
the time heater is on.

1694106287498.png


1694106467095.png


Regards, Dana.
 

kellys_eye

Jun 25, 2010
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If you use a Nano or Uno board timing is very accurate, as they both have xtal oscillator
on them.

Easy way is use mBlock to do the code. Here I have 3 inputs each with a button, a pullup,
and one output to drive NPN or MOSFET to control heater power. mBlock takes block
configuration and converts to Arduino code, then uses Arduino programmer to program board.

You could use 8 pin DIP ATTINY85 to do the job. Use UNO or Nano to program it.

Basically mBlock detects a key is down, then loops until its released, then invokes
the time heater is on.

View attachment 60676


View attachment 60677


Regards, Dana.
As much as I admire the versatility of such devices the post is 'gobble-de-gook' to me and, I'm sure, the OP too.

The KISS principle is important here.

Power switching is best achieved using MOSFETs rather than PNP/NPN (although that still works) as the losses, therefore component dissipation is very managable.

But keeping it even KISSier there's the likes of this:


or, for the more DIY inclined there's this:

 

danadak

Feb 19, 2021
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@kellys_eye
As much as I admire the versatility of such devices the post is 'gobble-de-gook' to me and, I'm sure, the OP too.

Roughly 8M kids here in US, starting in 6 th grade (typically) programming bots with it.
Not just mBlock either, now many visual programming languages. Codered, Visuino,
Scratch by MIT, Snap4arduino, Flowcode........ Hey MIT, thanks for your gobble-de-gook
work in this area, I know you are working on next gen.....

But I understand for a few this is a challenge.

But user, OP, already seems to be programming.

@OP, here is a more sophisticated timer/state machine, also in mBlock, that has
many triggers and easy to add states :


OP, if interested I will supply you with mBlock project for this.


Regards, Dana.
 
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danadak

Feb 19, 2021
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@OP, I was not paying attention to fact you wanted a cyclic routine of 40 on and the
selected off of 10 or 20 or 30, so corrected code.

1694171148984.png
This is what it would take :

1694170943320.png


Regards, Dana,
 
Last edited:

Delta Prime

Jul 29, 2020
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Scratch by MIT, Snap4arduino, Flowcode........ Hey MIT, thanks for your gobble-de-gook
What do you want it's an
" Arduino" made for third world countries. You could thank that fine institution for most everything else within 3 feet of you. Unless of course you are in a third world country then it'll probably be 6 ft away from you
 
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danadak

Feb 19, 2021
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What do you want it's an
" Arduino" made for third world countries. You could thank that fine institution for most everything else within 3 feet of you. Unless of course you are in a third world country then it'll probably be 6 ft away from you
The "gobble-de-gook" was referring to vacuous comment made in post #3.

MIT, and several others, is in fact WW contributor for sure. As are several in
Germany, England, Japan, France,........


Regards, Dana.
 

kellys_eye

Jun 25, 2010
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The "gobble-de-gook" was referring to vacuous comment made in post #3.
I see nothing 'vacuous' in trying to KISS or simplify a solution.

The current 'insistence' that everything needs to reduced to a microcontroller and code is wearing. For many people this would mean learning to code, obtaining the hardware to load the code to a processor, buying the processor and associated electronics/construction material, housing the finished project and then (usually) debugging the code.

All that to simply 'switch on and off at intervals' - all achieved using the ready-made, simple to wire, no accessories required module as linked to in that reply. That is not a complicated process and over-engineering it to display prowess in a subject doesn't help the end user.

If the intent is to encourage people to take up coding, using a particular coding method and demonstrate the versatility of the whole exercise then congratulations, you might have achieved that end purpose.

But if the intent is to actually do what is required, simply, easily, cheaply and quickly I think the microprocessor route is OTT.

Hence my suggestion to KISS.
 

danadak

Feb 19, 2021
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The current 'insistence' that everything needs to reduced to a microcontroller and code is wearing. For many people this would mean learning to code, obtaining the hardware to load the code to a processor, buying the processor and associated electronics/construction material, housing the finished project and then (usually) debugging the code.

Seemed to me the OP was familiar with Arduino. And I assumed coding unless he was using it as a heater.

All that to simply 'switch on and off at intervals' - all achieved using the ready-made, simple to wire, no accessories required module as linked to in that reply. That is not a complicated process and over-engineering it to display prowess in a subject doesn't help the end user.

I may have misinterpreted goals but think, until OP corrects me, that there is one cyclic timing
interval with a specific selectable real time parameter of the off time. So module must take OP
random input and change its off time in the cycle and keep repeating the new cycle. As far as
prowess I am in the age group where I think answering a question is also an opportunity to show
alternative methods. And I think of a UP as an OpAmp, a Regulator, in the pantheon of
solution parts. The new KISS. Yes I would agree, using modules, if they handle all the requirements,
is rapid solution, in this case since OP was asking for alternative design approach to Arduino,
seeking simplicity, opportunity to show how simple and fast it is with block programming . As
far as prowess I yield to the 6'th graders doing robots. Note the Arduino he has is useful as a
programmer for ATTINY85 like parts. Takes a couple of extra steps, violating the KISS rule,
but for us human mollusks not too great a burden.

Hence my suggestion for block programming and ATTINY85.

Regards, Dana.
 

lostbit01

Sep 7, 2023
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Thank all for your input, i know an Arduino can work and I can write the sketch for it.
But I like to learn things by doing and making this with transistors was my goal.
 

AnalogKid

Jun 10, 2015
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I see nothing 'vacuous' in trying to KISS or simplify a solution.

Completely agree.

The current 'insistence' that everything needs to reduced to a microcontroller and code is wearing.

Now you've stepped in it. When I first started bouncing around forums, it seemed like every other "solution" completely ignored the OP's skill level and/or design requirements, and went straight to either a uC or a 555. Hence, my tagline is "Maslow Antagonist". Here's why:

"I suppose it is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail."

- Abraham Maslow, Professor of Psychology at Brandeis University
"The Psychology of Science: A Reconnaissance", 1966

ak
 

AnalogKid

Jun 10, 2015
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The "gobble-de-gook" was referring to vacuous comment made in post #3.

Hold on there, sparky. "vacuous" - ? Not even close.

In fact, his comment conveyed *the value of your response to him* with clarity and precision, so it had useful substance, the exact opposite of a vacuum; something your response to him lacked.

He did not understand your response, while you clearly understood his. Now, which one is vacuous?

ak
 

AnalogKid

Jun 10, 2015
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But I digress . . .

Your max overall timing period is 70 seconds. That is a bit long for a simple R-C timer, but not terrible. 1% tolerance resistors are cheap, and 1% tolerance capacitors are reasonably priced at Mouser. The CMOS version of a 555 (LMC555) has much higher input impedances, so you can use higher resistor values to keep the capacitor size down. As with much in the life of electronics, the capacitor is the majority of the problem.

For a simple, direct-drive approach, where the oscillator drives the heater load directly, a 555 is the best. It was designed specifically so that it contributes almost nothing to the overall error budget of the circuit. In 1972, 1% resistors were expensive and 5% tolerance, precision high-value capacitors were insane, and trimpots were unliked. The idea behind the 555 was that all (ok, almost all) of the circuit errors were in the external components; you didn't have to tweak the circuit because of chip-to-chip performance variations.

AND, your comment about PNP transistors in your application is incorrect. As a saturated switch, the base does indeed need to be more negative than the emitter; BUT when configured as a high-side switch, that means the emitter is a +12 V and the base is at +11.x V. "Pulled down" and pulled below ground are two entirely different things.

Without changing to a crystal oscillator, the easiest way to improve timing accuracy is to add a divider stage between the oscillator and the load switch. This can be any decimal or binary divider. The higher the divide ratio, the smaller the values of the R and C timing components (and it's all about the C). A tempting solution is the CD4060, which is an oscillator and divider all in one chip. The problem with it is that its oscillator is not as stable as a 555's, so there is some precision loss that offsets the precision gained by its higher oscillator frequency.

Chew on all of that and give us some more guidance about what you would like to try, your skill set for assembling a small circuit, etc.

Off to see The Buckeyes beat up someone. Schematics later if no one has jumped in with some.

ak
 

danadak

Feb 19, 2021
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Thank all for your input, i know an Arduino can work and I can write the sketch for it.
But I like to learn things by doing and making this with transistors was my goal.
I am glad we all could help you with ideas, psycho analysis, irrelevant
void filling....

Be not afraid of the eye, he even helped me, looks like based on extensive
analysis post # 3 was double vacuous per the logic.

Regards, Dana.
 

lostbit01

Sep 7, 2023
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Well the new dew heater band is only 18 ohms so the transistors are going to get verry hot!
I tried 555 timer with a small NPN transistor to fast trigger the relay and that is working. Ill need to play
with astable time adjustments.
Thanks everyone.
 
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