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555 woes (monostable oscillator)

I'm trying to do a simple 555 circuit and can't seem to get a square
wave on my output.

I'm using the circuit found at http://home.cogeco.ca/~rpaisley4/LM555.html#3
and am using 1.5K for R1, 5K for R2 and a 47 uF for C (although my
radio shack meter says its a 59 uF).

The output I'm trying to read on a 20 MHz oscope shows a slight ripple
in the millivolt range, but no square wave.

I know its an open collector output, so I put a 10K pullup resistor to
the 5 volt rail, but still no square wave.

Its possible that I'm not using my o-scope correctly because I just
got it on ebay. It does seem to read correctly for the 5 volt supply
as well as another 24 volt supply, but thats just DC volts, no wave
form.

Other points to note,

* The 1.5K on R1 has a 15 turn pot
* The 5 K is actually 2 10K's in parallel
* This chip is a 556 (dual timer) but I have made sure to remap the
pinouts.
* I'm running Vcc of 5 volts.

Any suggestions would be greatly appreciated.

Thanks.
 
M

MooseFET

Jan 1, 1970
0
On May 25, 6:21 pm, [email protected] wrote:
[... about LM555 ...]
Google on LM555 and datasheet, you are likely to find better
information about the chip.

I'm using the circuit found athttp://home.cogeco.ca/~rpaisley4/LM555.html#3
and am using 1.5K for R1, 5K for R2 and a 47 uF for C (although my
radio shack meter says its a 59 uF).

The output I'm trying to read on a 20 MHz oscope shows a slight ripple
in the millivolt range, but no square wave.

What voltage (DC), do you see on pin 2, pin 6 and pin 3?

If pin 2 is less than 1/3 Vcc, the output should go high
If pin 6 is more than 2/3 Vcc, the output should go low.

Which isn't it doing?


I know its an open collector output, so I put a 10K pullup resistor to

No, the pin 7 is th eopen collector. Pine 3 is push pull.
 
J

Jamie

Jan 1, 1970
0
I'm trying to do a simple 555 circuit and can't seem to get a square
wave on my output.

I'm using the circuit found at http://home.cogeco.ca/~rpaisley4/LM555.html#3
and am using 1.5K for R1, 5K for R2 and a 47 uF for C (although my
radio shack meter says its a 59 uF).

The output I'm trying to read on a 20 MHz oscope shows a slight ripple
in the millivolt range, but no square wave.

I know its an open collector output, so I put a 10K pullup resistor to
the 5 volt rail, but still no square wave.

Its possible that I'm not using my o-scope correctly because I just
got it on ebay. It does seem to read correctly for the 5 volt supply
as well as another 24 volt supply, but thats just DC volts, no wave
form.

Other points to note,

* The 1.5K on R1 has a 15 turn pot
* The 5 K is actually 2 10K's in parallel
* This chip is a 556 (dual timer) but I have made sure to remap the
pinouts.
* I'm running Vcc of 5 volts.

Any suggestions would be greatly appreciated.

Thanks.
to my knowledge the 555 does not have an open collector on
the output..
Try putting the input of your scope on DC and use the
10:1 setting on the probe.
 
S

Stanislaw Flatto

Jan 1, 1970
0
I'm trying to do a simple 555 circuit and can't seem to get a square
wave on my output.

I'm using the circuit found at http://home.cogeco.ca/~rpaisley4/LM555.html#3
and am using 1.5K for R1, 5K for R2 and a 47 uF for C (although my
radio shack meter says its a 59 uF).

The output I'm trying to read on a 20 MHz oscope shows a slight ripple
in the millivolt range, but no square wave.

I know its an open collector output, so I put a 10K pullup resistor to
the 5 volt rail, but still no square wave.

Its possible that I'm not using my o-scope correctly because I just
got it on ebay. It does seem to read correctly for the 5 volt supply
as well as another 24 volt supply, but thats just DC volts, no wave
form.

Other points to note,

* The 1.5K on R1 has a 15 turn pot
* The 5 K is actually 2 10K's in parallel +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
* This chip is a 556 (dual timer) but I have made sure to remap the
pinouts.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Check, recheck and have someone certify your corrections and findings.
Advice: get/buy/steal single 555 and start from there.
* I'm running Vcc of 5 volts.

Any suggestions would be greatly appreciated.

Thanks.

HTH

Stanislaw.
 
B

Bruce Varley

Jan 1, 1970
0
I'm trying to do a simple 555 circuit and can't seem to get a square
wave on my output.

I'm using the circuit found at
http://home.cogeco.ca/~rpaisley4/LM555.html#3
and am using 1.5K for R1, 5K for R2 and a 47 uF for C (although my
radio shack meter says its a 59 uF).

The output I'm trying to read on a 20 MHz oscope shows a slight ripple
in the millivolt range, but no square wave.

I know its an open collector output, so I put a 10K pullup resistor to
the 5 volt rail, but still no square wave.

Its possible that I'm not using my o-scope correctly because I just
got it on ebay. It does seem to read correctly for the 5 volt supply
as well as another 24 volt supply, but thats just DC volts, no wave
form.

Other points to note,

* The 1.5K on R1 has a 15 turn pot
* The 5 K is actually 2 10K's in parallel
* This chip is a 556 (dual timer) but I have made sure to remap the
pinouts.
* I'm running Vcc of 5 volts.

Any suggestions would be greatly appreciated.

Thanks.

I haven't checked your reference, but from the description I assume you want
a square wave generator rather than a triggered monostable. If you're not
locked into a 555 and can accept a duty cycle that's not exactly (but close
to) 50%, then you can make an extremely simple squarewave generator out of a
CMOS schmitt inverter, such as the 74HC14. Take one of the gates, R from
output to input and C from input to 0V. That's all. Many datasheets provide
the equation for calculating R and C for a required period, or maybe someone
here could oblige....? If you don't need the other 5 gates, don't forget to
tie the unused inputs to one or other rail. Or you can run several of them
in parallel as a buffer to increase the drive capacity.
 
P

Paul E. Schoen

Jan 1, 1970
0
I'm trying to do a simple 555 circuit and can't seem to get a square
wave on my output.

I'm using the circuit found at
http://home.cogeco.ca/~rpaisley4/LM555.html#3
and am using 1.5K for R1, 5K for R2 and a 47 uF for C (although my
radio shack meter says its a 59 uF).

The output I'm trying to read on a 20 MHz oscope shows a slight ripple
in the millivolt range, but no square wave.

I know its an open collector output, so I put a 10K pullup resistor to
the 5 volt rail, but still no square wave.

Its possible that I'm not using my o-scope correctly because I just
got it on ebay. It does seem to read correctly for the 5 volt supply
as well as another 24 volt supply, but thats just DC volts, no wave
form.

Other points to note,

* The 1.5K on R1 has a 15 turn pot
* The 5 K is actually 2 10K's in parallel
* This chip is a 556 (dual timer) but I have made sure to remap the
pinouts.
* I'm running Vcc of 5 volts.

Any suggestions would be greatly appreciated.

Thanks.

You *do* realize that for a *monostable* pulse generator you must keep
clicking the switch to get a square wave? The pulse will be just 250 mSec
wide. If you have the astable circuit (which I see is #3), then it should
oscillate.

Make sure you have a good bypass capacitor on the 5 VDC supply. It is not
shown in the schematic but is critical for reliable operation.

Good luck,

Paul
 
D

D from BC

Jan 1, 1970
0
I'm trying to do a simple 555 circuit and can't seem to get a square
wave on my output.

I'm using the circuit found at http://home.cogeco.ca/~rpaisley4/LM555.html#3
and am using 1.5K for R1, 5K for R2 and a 47 uF for C (although my
radio shack meter says its a 59 uF).

The output I'm trying to read on a 20 MHz oscope shows a slight ripple
in the millivolt range, but no square wave.

I know its an open collector output, so I put a 10K pullup resistor to
the 5 volt rail, but still no square wave.

Its possible that I'm not using my o-scope correctly because I just
got it on ebay. It does seem to read correctly for the 5 volt supply
as well as another 24 volt supply, but thats just DC volts, no wave
form.

Other points to note,

* The 1.5K on R1 has a 15 turn pot
* The 5 K is actually 2 10K's in parallel
* This chip is a 556 (dual timer) but I have made sure to remap the
pinouts.
* I'm running Vcc of 5 volts.

Any suggestions would be greatly appreciated.

Thanks.


Getting beat up by a 555...omg... :p

If R1 is turned to 0 ohms then the cap cannot discharge.
(Assuming R1 connects between the discharge pin and V+).
The astable cct will not oscillate.
Does the 555 get hot?
Make sure R1 is turned to something the 555 can tolerate.
D from BC
 
S

Spehro Pefhany

Jan 1, 1970
0
On 25 May 2007 18:21:08 -0700, the renowned
I'm trying to do a simple 555 circuit and can't seem to get a square
wave on my output.

I'm using the circuit found at http://home.cogeco.ca/~rpaisley4/LM555.html#3
and am using 1.5K for R1, 5K for R2 and a 47 uF for C (although my
radio shack meter says its a 59 uF).

The output I'm trying to read on a 20 MHz oscope shows a slight ripple
in the millivolt range, but no square wave.

I know its an open collector output, so I put a 10K pullup resistor to
the 5 volt rail, but still no square wave.

Its possible that I'm not using my o-scope correctly because I just
got it on ebay. It does seem to read correctly for the 5 volt supply
as well as another 24 volt supply, but thats just DC volts, no wave
form.

Other points to note,

* The 1.5K on R1 has a 15 turn pot
* The 5 K is actually 2 10K's in parallel
* This chip is a 556 (dual timer) but I have made sure to remap the
pinouts.
* I'm running Vcc of 5 volts.

Any suggestions would be greatly appreciated.

Thanks.


Is it a CMOS version (eg. LMC555, TLC555 7555) rather than
LM555/NE555? If so, you *must* tie 4 to Vcc. Otherwise, it's just a
really good idea.

You're only expecting to get a single pulse when the switch is
pressed, right?

These questions really belong in sci.electronics.basics, BTW.


Best regards,
Spehro Pefhany
 
D

Don Lancaster

Jan 1, 1970
0
I'm trying to do a simple 555 circuit and can't seem to get a square
wave on my output.

I'm using the circuit found at http://home.cogeco.ca/~rpaisley4/LM555.html#3
and am using 1.5K for R1, 5K for R2 and a 47 uF for C (although my
radio shack meter says its a 59 uF).

The output I'm trying to read on a 20 MHz oscope shows a slight ripple
in the millivolt range, but no square wave.

I know its an open collector output, so I put a 10K pullup resistor to
the 5 volt rail, but still no square wave.

Its possible that I'm not using my o-scope correctly because I just
got it on ebay. It does seem to read correctly for the 5 volt supply
as well as another 24 volt supply, but thats just DC volts, no wave
form.

Other points to note,

* The 1.5K on R1 has a 15 turn pot
* The 5 K is actually 2 10K's in parallel
* This chip is a 556 (dual timer) but I have made sure to remap the
pinouts.
* I'm running Vcc of 5 volts.

Any suggestions would be greatly appreciated.

Thanks.
The 555 has been obsolete for two decades now.
Use a PIC instead.


--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com
 
P

Paul E. Schoen

Jan 1, 1970
0
Spehro Pefhany said:
On 25 May 2007 18:21:08 -0700, the renowned



Is it a CMOS version (eg. LMC555, TLC555 7555) rather than
LM555/NE555? If so, you *must* tie 4 to Vcc. Otherwise, it's just a
really good idea.

You're only expecting to get a single pulse when the switch is
pressed, right?

These questions really belong in sci.electronics.basics, BTW.


Best regards,
Spehro Pefhany

Yes, the reset pin 4(4,10 for 556) is not shown as connected in the
schematic, and is almost always connected directly to pin 8(14 on 556). The
equivalent schematic for the LM556 does not show an internal pullup on this
pin.

Also, the control voltage pin 5(3,11 on 556) should be bypassed with a
capacitor. Makes it more stable if the power supply is noisy. Tell us what
voltages you read at each of the pins on your 556. Might as well fix this
here rather than moving to SEB.

Paul
 
D

D from BC

Jan 1, 1970
0
The 555 has been obsolete for two decades now.
Use a PIC instead.

Oh come on...
Has mixed mode electronics gotten that PICy?

D from BC
 
F

Fred Bloggs

Jan 1, 1970
0
I'm trying to do a simple 555 circuit and can't seem to get a square
wave on my output.

I'm using the circuit found at http://home.cogeco.ca/~rpaisley4/LM555.html#3
and am using 1.5K for R1, 5K for R2 and a 47 uF for C (although my
radio shack meter says its a 59 uF).

The output I'm trying to read on a 20 MHz oscope shows a slight ripple
in the millivolt range, but no square wave.

I know its an open collector output, so I put a 10K pullup resistor to
the 5 volt rail, but still no square wave.

Its possible that I'm not using my o-scope correctly because I just
got it on ebay. It does seem to read correctly for the 5 volt supply
as well as another 24 volt supply, but thats just DC volts, no wave
form.

Other points to note,

* The 1.5K on R1 has a 15 turn pot
* The 5 K is actually 2 10K's in parallel
* This chip is a 556 (dual timer) but I have made sure to remap the
pinouts.
* I'm running Vcc of 5 volts.

Any suggestions would be greatly appreciated.

Thanks.

Your component values yield an oscillation frequency of about 4Hz, so
you will want something like 100ms per division time scale to view the
pulse train.
 
F

Fred Bloggs

Jan 1, 1970
0
Spehro said:
On 25 May 2007 18:21:08 -0700, the renowned




Is it a CMOS version (eg. LMC555, TLC555 7555) rather than
LM555/NE555? If so, you *must* tie 4 to Vcc. Otherwise, it's just a
really good idea.

You're only expecting to get a single pulse when the switch is
pressed, right?

These questions really belong in sci.electronics.basics, BTW.


Best regards,
Spehro Pefhany

Is there a CMOS 556? Sounds rare...
 
F

Fred Bloggs

Jan 1, 1970
0
Spehro said:
Not rare. TLC556; about 30,000 in stock at Digikey. Probably others.


Best regards,
Spehro Pefhany

I see, and minimum astable frequency of 1.2MHz at 5V too...looks like
someone is using a lot of these "hobby" chips.
 
S

Spehro Pefhany

Jan 1, 1970
0
Is there a CMOS 556? Sounds rare...

Not rare. TLC556; about 30,000 in stock at Digikey. Probably others.


Best regards,
Spehro Pefhany
 
D

D from BC

Jan 1, 1970
0
I see, and minimum astable frequency of 1.2MHz at 5V too...looks like
someone is using a lot of these "hobby" chips.

555's are for kids..
Now PIC's..that the Arrfff! Arrrfff! muscle machine of choice... :)

However..
I don't care if 555's have a newbieish reputation, sometimes they fit
the problem and I include them in designs.
D from BC
 
R

Rich Grise

Jan 1, 1970
0
[email protected] wrote:
The 555 has been obsolete for two decades now.
Use a PIC instead.

There's a new rule here in the s.e.* hierarchy. Nobody's allowed to say
"Use a Pic" without providing a circuit and a program. ;-)

Cheers!
Rich
 
D

D from BC

Jan 1, 1970
0
There's a new rule here in the s.e.* hierarchy. Nobody's allowed to say
"Use a Pic" without providing a circuit and a program. ;-)

Cheers!
Rich

For example:

Use a PIC!
Put 2 resistors on an I/O pin..
Here's the code:

INCF FSR, 0x1
INCF INDF, 0x1
MOVLW 0x22
XORWF INDF, 0
BTFSS STATUS, 0x2
GOTO detdone
CALL rndgen
GOTO chgmode

Have a nice day! :)
D from BC
 
P

Paul E. Schoen

Jan 1, 1970
0
D from BC said:
For example:

Use a PIC!
Put 2 resistors on an I/O pin..
Here's the code:

INCF FSR, 0x1
INCF INDF, 0x1
MOVLW 0x22
XORWF INDF, 0
BTFSS STATUS, 0x2
GOTO detdone
CALL rndgen
GOTO chgmode

Have a nice day! :)
D from BC

You don't need code (or even program the PIC*) to make an oscillator. Just
use the clock pins and add whatever RC network you like for the frequency
on GP4. The PIC12F629 has the RC mode as default, and the CLKOUT is fOsc/4
on GP5. You can eliminate the R and C if you set the clock mode to
internal, but then you only have a 4 MHz clock with 1 MHz output.

*(Maybe you have to set the GP5 pin as output)

Of course it won't have the drive capability of the 555 :)

Paul
 
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