This is my 4th 555 timer construction with the same results. I used an NE555 twice and an LMC555 twice, both with consistent results and all purchased from Digikey. I am using a 12vdc regulated power supply. Schematic attached. Pin 3 will go to an optocoupler, but for testing purposes, I am using a standard LED. Target is 1Hz. I build the first ones on a breadboard using a 9v battery for convience and then move to soldering a perf board as the final. After the first two, I thought I may have over heated the timers, so I started using a DIP socket for the 555 and still got the same results. After my 4th Perf board, I decided to see what the results would be if I connected the 12v supply to the bread board, which was the only variable. I am using the Hz setting on a multimeter and visual for measurements.

These are the results;

Bread Board: 9v 1.02Hz Visual LED 1Hz Great Stuff !
12v 5kHz Visual LED 1Hz ???????

Perf Board: 9v 50Hz Visual LED constantly on
12v 5kHz Visual LED constantly on

I soldered each perf board without referring back to the previous one and just focused on the schematic. I am now the proud owner of four perf boards that operate exactly the same.

Any thoughts would be appreciated.

 

This is my 4th 555 timer construction with the same results. I used an NE555 twice and an LMC555 twice, both with consistent results and all purchased from Digikey. I am using a 12vdc regulated power supply. Schematic attached. Pin 3 will go to an optocoupler, but for testing purposes, I am using a standard LED. Target is 1Hz. I build the first ones on a breadboard using a 9v battery for convience and then move to soldering a perf board as the final. After the first two, I thought I may have over heated the timers, so I started using a DIP socket for the 555 and still got the same results. After my 4th Perf board, I decided to see what the results would be if I connected the 12v supply to the bread board, which was the only variable. I am using the Hz setting on a multimeter and visual for measurements.

These are the results;

Bread Board: 9v 1.02Hz Visual LED 1Hz Great Stuff !
12v 5kHz Visual LED 1Hz ???????

Perf Board: 9v 50Hz Visual LED constantly on
12v 5kHz Visual LED constantly on

I soldered each perf board without referring back to the previous one and just focused on the schematic. I am now the proud owner of four perf boards that operate exactly the same.

Any thoughts would be appreciated.

Post photos of breadboard and front/back of a perf board.

 

What frequency reading do you get if you connect the multimeter directly to the 12V supply?
It sounds like the meter is picking noise from the PSU.

 

Your timing equations are not quite correct. D1 does isolate R2 from the charge-up part of the timing cycle, but it also introduces a 0.6 V term into the voltage equation.. This affects the equation for the frequency. Because R1 is such a small percentage of R2, the error is small. Is there a reason you need such a small duty cycle? This might affect the ability of your meter to read the frequency accurately.

ak

 

Post photos of breadboard and front/back of a perf board.

The plan is to have a second 555 on the left side as well

 

Your timing equations are not quite correct. D1 does isolate R2 from the charge-up part of the timing cycle, but it also introduces a 0.6 V term into the voltage equation.. This affects the equation for the frequency. Because R1 is such a small percentage of R2, the error is small. Is there a reason you need such a small duty cycle? This might affect the ability of your meter to read the frequency accurately.

ak

The small duty cycle is to reduce the amount of current that a capacitor will discharge through the opto. when the 555 fires. The meter does read correctly on the bread board with 9V.

 

What frequency reading do you get if you connect the multimeter directly to the 12V supply?
It sounds like the meter is picking noise from the PSU.

Such an interesting question and a more interesting answer. I get 5kHz. What the ?

 

Is the power supply switch mode?
I'd bet that it is and I could hazard a guess at its operating frequency.

 

I am using the Hz setting on a multimeter

Run-of-the-mill multimeters expect a decent sine-wave input to determine frequency, and give unreliable/misleading readings for other waveforms.

 

Is the power supply switch mode?
I'd bet that it is and I could hazard a guess at its operating frequency.

Sorry, but I don't know what "switch mode" is. It is called a "Switch Power Supply". Putting the probe on its output, I get 179Hz. I am experimenting with both a 12v 3A wall wort which shows 5kHz and a HS-150-12 power supply 12A, 150W. Both generate the same problem.

 

Switch mode supplies work by rectifying the mains, then chopping the DC into a transformer. As the frequency is higher the transformer can be smaller and lighter than a regular mains transformer. They are also more efficient than linear supplies. However, it is very difficult to get rid of the switching spikes from the output and that is what your meter is reading.
https://en.wikipedia.org/wiki/Switched-mode_power_supply

 

You ALWAYS build a prototype using BATTERIES.

 

You ALWAYS build a prototype using BATTERIES.

I don't; never have, never will. Why waste batteries?

 

"I don't; never have, never will. Why waste batteries?"

You have obviously not built thousands of circuits. Try building an FM transmitter using a power supply.

That's why I only teach 18 year-olds.

 

You have obviously not built thousands of circuits. Try building an FM transmitter using a power supply.

What does that have to do with always using batteries when building prototypes????

 

"What does that have to do with always using batteries when building prototypes???? "


That's why I only teach 18 year-olds.

 

That's why I only teach 18 year-olds.

Why insult 18 year olds??

 

You ALWAYS build a prototype using BATTERIES.

I always use a power supply that doesn't suck.

ak

 

I NEVER use batteries when developing stuff- UNLESS the final device REQUIRES batteries.
Even then, I test with batteries AFTER I get it all working on a bench supply.

Batteries add yet another variable that you just shouldn't need to think about.