Question RE: NE555 pulse generator

[ericgibbs]

I am still having the same problem with the voltage drop from the input to the output of the 555 chip when the relay is connected. The input is about 6.5V and the output is about 4V.

I guess I am still looking for ideas on how to correct this. It seems I am getting conflicting information regarding adding the transistor and diode circuitry. I have the transistor but don't want to solder it on until I am fairly sure that this will work.

hi DW,
Look at this circuit.
The 100R and 12Vz will reduce the voltage to the NE555 to 12V

What is the electrical spec for the counter.??

Are you using a TLC555 CMOS or NE555 TTL

 

[dwhitt]

That is normal. You have a 1k resistor in series with the power to the circuit so the supply voltage of the C555 is jumping up and down.
Also the Cmos 555 has a very low output current so it has a high output voltage loss.

Don't you still have a solid-state relay with a minimum input voltage of 3V?

Yes, but the output also goes to the timer/counter. The counter's input is 12V. And the problem is the counter isn't counting as it should because the input voltage is only 4V.

The 1K resistor was to step down the voltage because the 15.4V that comes from the transformer was too high for the chip and I kept burning them up.

Here is what I want to try now. (But it will have to wait until tomorrow for me to make yet another run to the store.) I want to take out the 1k Ohm resistor at the beginning of my circuit. And change the 15V power supply with a 12V power supply. I am hoping that the 12V power supply will be enough to run the circuit without blowing any more chips. I will let you guys know tomorrow how it turns out. In the mean time please feel free to offer any additional input or suggestions. Thanks again for all your help.

BTW, I am not a he as some of you referred to me earlier.

 

[ericgibbs]

And change the 15V power supply with a 12V power supply. I am hoping that the 12V power supply will be enough to run the circuit without blowing any more chips. I will let you guys know tomorrow how it turns out. In the mean time please feel free to offer any additional input or suggestions. Thanks again for all your help.

BTW, I am not a he as some of you referred to me earlier.

hi,
With a 12Vdc reg psu the 100R and12Vz are not required in my circuit.

Tell me the current rating of the counter, I know its 12V and we can use a transistor to drive it OK.?

 

[dwhitt]

hi DW,
Look at this circuit.
The 100R and 12Vz will reduce the voltage to the NE555 to 12V

What is the electrical spec for the counter.??

What is the 12Vz 0.5W symbol? Is that a voltage regulator?

The counter/timer specs:
power supply: 12-24VDC
Operational Voltage: 90-110%
power consumption: about 4VA
Max counting speed 2k cps
min signal width: min 20ms
Input: Impedance by shot

Circuiting contacs: Max 1KΩ
Residual voltage: Max 0.5V
IMpedance by opening: Mon 100kΩ
Input Impedance: 20kΩ​

I am not sure if I explained this or not but the 6.2V I had in my schematic was just the measured amount I got from my Voltmeter.

It looks like you added some additional capacitance between the Vcc and ground on the chip? Then upped the capacitance between pins 6 and ground? Will this stabalize the wave form?

 

[dwhitt]

hi DW,
Look at this circuit.
The 100R and 12Vz will reduce the voltage to the NE555 to 12V

What is the electrical spec for the counter.??

Are you using a TLC555 CMOS or NE555 TTL

Oh, and it is a TLC555 CMOS. Thanks again for taking the time to look at this!

 

[BrownOut]

I guess I am still looking for ideas on how to correct this. It seems I am getting conflicting information regarding adding the transistor and diode circuitry. I have the transistor but don't want to solder it on until I am fairly sure that this will work.

When we suggested that, you had given us very little information about the devices you were using. After you showd us the SS relay, we agreed that the transistor and diode weren't needed.

 

[ericgibbs]

Oh, and it is a TLC555 CMOS. Thanks again for taking the time to look at this!

Hi,
Looking at the counter 4VA at 12V thats approx 330mA.

So the transistor will drive the counter.

Look at this simulation.

OK.?

EDIT:
R3 36R represents the counter.

 

[dwhitt]

When we suggested that, you had given us very little information about the devices you were using. After you showd us the SS relay, we agreed that the transistor and diode weren't needed.

Sorry, I hope I didn't offend. I really appreciate everyone's input with this. I just wanted to make sure it was a general consensus among all the experts before continuing. At the time when I wrote that comment, I didn't realize that everyone had agreed on that issue.

Hi,
Looking at the counter 4VA at 12V thats approx 330mA.

So the transistor will drive the counter.

Look at this simulation.

OK.?

EDIT:
R3 36R represents the counter.

Hmmm. interesting. This may take a while for me to digest. But it looks like it will almost be a redo for me. Just scrapping my design and starting over.

One question comes to mind though (and I know I am going backwards when I ask this) but it seems you interpreted 37msec pulse width to mean something different. The instructions I have says "The pulse test box should be calibrated for an output pulse width of 37msec." At first I interpreted it to mean as what you have (the total wavelegth to be 37msec). But then as I read the instructions of the complete test I think it means that it needs to be "on" for 37msec.

 

[ericgibbs]

Hmmm. interesting. This may take a while for me to digest. But it looks like it will almost be a redo for me. Just scrapping my design and starting over.

One question comes to mind though (and I know I am going backwards when I ask this) but it seems you interpreted 37msec pulse width to mean something different. The instructions I have says "The pulse test box should be calibrated for an output pulse width of 37msec." At first I interpreted it to mean as what you have (the total wavelegth to be 37msec). But then as I read the instructions of the complete test I think it means that it needs to be "on" for 37msec.

hi,
The basic 555 circuit is the same, its just the SSR drive and counter drive transistor... ignore the rightside of the circuit thats just a simulated SSR to keep me happy.

The transistor can be any 1amp npn device with a gain of about 50 at 330mA.

Ref the pulse width use the components that give you the pulse width that you need. I went for a total period of about 37mSec.

So its actually High for 37mS, low for 37mS thats required.

Have fun.!

If you need any more help, just ask.

 

[dwhitt]

Thank you so much. I think I see what you are doing here. Basically the input to the counter will be the opposite of the Vout. That is ok because the counter I can change to count the "Ups" or the "downs".

Looks like I still need to change to a 12VDC power supply.

What is the diode and R6 for?

ETA: Also, is the D2 part of the simulated counter or does that need to be added as well?

 

[ericgibbs]

Thank you so much. I think I see what you are doing here. Basically the input to the counter will be the opposite of the Vout. That is ok because the counter I can change to count the "Ups" or the "downs".

Looks like I still need to change to a 12VDC power supply.

What is the diode and R6 for?

ETA: Also, is the D2 part of the simulated counter or does that need to be added as well?

hi,
Youre right about the ups/downs.
A 12Vdc regulated supply is required at least 500mA rating.

The Counter is most likely a solenoid, as Im not sure, [there maybe an internal transistor] the diode is there to protect the transistor.

Look at this image of the 37mS timing, I would split the 100K into two parts, say a 82K fixed resistor and a 50k variable resistor. This will enable adjustment of the timing.

R6 and the LED are the power ON indicator. Dont use a lamp.!

 

[dwhitt]

As with most projects, the criteria has changed and I had to redo my board almost entirely. Instead of an astable operation, they now want a monostable operation. Here is the new definition of my problem:

They want a 37msec single pulse (generated by the 555 chip) to do two things: 1) send a signal to a counter to count the number of pulses, and 2) turn on a relay for the same 37 msec. After the pulse the relay should go back to zero. The pulses are commanded by pressing a button.

Here is the schematic that I came up with however it isn't working like I think it *should* work. From what i have read the trigger on the 555 IC is negatively triggered. That is why I had the NC button. However, when I press the button (breaking the contact to the trigger input) what I get is sporatic, nonreproducable results. Sometimes I get 10-20 pulses, and sometimes I get no pulses at all.

The other problem is that there is somehow some around 3V at the input of the relay when the trigger is still HIGH (meaning there should not be a pulse being sent)???

Any advise or words of wisdom?? Thanks in advance.

 

[BrownOut]

1) You didn't post your schematic
2) Who are "they"?

 

[dwhitt]

1) You didn't post your schematic
2) Who are "they"?

Oops sorry. Wrong file type. I corrected it.

"They" are the powers that be (aka my bosses)

 

[ericgibbs]

Oops sorry. Wrong file type. I corrected it.

"They" are the powers that be (aka my bosses)

hi DW,
I guess the relay is still SSR.?? and the electromechanical counter is the same.?


BTW: your circuit will not work.

 

[dwhitt]

hi DW,
I guess the relay is still SSR.?? and the electromechanical counter is the same.?

Yes. that would be correct.

 

[ericgibbs]

Yes. that would be correct.

hi DW,
Have a look at this 37mSec Mono.

 

[audioguru]

Please do not label your TLC555 (it has low power Cmos) an NE555 (it has high power bipolar transistors). They are completely different.

Pin 2 must go low to trigger the timer. Your pin 2 never goes low.

 

[dwhitt]

hi DW,
Have a look at this 37mSec Mono.

Thanks Eric. Is that a pnp transistor? I am using an npn ?

I don't quite understand what you are doing with the Myswitch? It looks like the trigger will go to ground when you push the trigger PB, but I am not understanding the symbology? Are you connecting the common of the button to the trigger, 12V to the NC side and ground to the Open terminal?

I have a friend who came across an old pulse test box and he gave me the transistor circuitry that is in my schematic. I was trying to match what he had even though he didn't know the exact circuitry outside the 555 chip. He was also able to provide the part number for the SSR. I'm guessing there is more than one right answer to this problem. I want to try the schematic you provided but I currently do not have the diodes. So I will have to go back to the store for those before I can test your schematic. I do appreciate all the time you have put into this.

Please do not label your TLC555 (it has low power Cmos) an NE555 (it has high power bipolar transistors). They are completely different.

Pin 2 must go low to trigger the timer. Your pin 2 never goes low.

Oops, sorry I did make the correction in my schematic in regards to the naming of the chip.

I guess I left this out in my previous posts, but I did connect the trigger to ground during my test and it still acted sporatic with unrepeatable results.

 

[ericgibbs]

hi,
Is this better.?

npn transistor and the push button.

Remember the SSR in my dwg is for simulation.

Connect the OUT to the 'real' SSR +in terminal and the SSR -in to the 0V line.