Originally Posted by BrownOut

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.

Originally Posted by ericgibbs

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.

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.

Originally Posted by BrownOut

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)

Originally Posted by ericgibbs

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

Yes. that would be correct.

Originally Posted by ericgibbs

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.

Originally Posted by 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.

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.