cannot reliably toggle flipflop when driven by phototransistor circuit

Might be a bit overkill, but you could use the opto to trigger a 2nd 555 wired as a monostable to drive the JK CLK

Stumbled onto the fix soon after writing the above, I put a 22k resistor in series between the buffer output and the flipflop clock input and this solved the problem.

But, still misses 1 out of every 50 pulses. Any gurus out there with experience of this?

Finally, for the sake of somebody else with a similar circuit, the buffer output is placed as close to the flip flop clk input as possible then tie the buffer (invertor in this case) output to ground thru a

0.1uf cap(multilayer ceramic chip) and then run a 5.1k resistor to connect it to the clk input, works great.

The Voltage levels must not be the same - if connecting a DVM improves things slightly it sounds like the voltage is not going low enough.

what have you used to measure this signal ? if you have not used a CRO then you cannot know what is really happening here.

you may need to feed the signal through a schmitt trigger (my favourite is the 74LS14 ) to ensure that it is toggling correctly - either way you need to look at the signal with an Oscilloscope

Regards Richard Freeman

Look at the signal with a CRO - it is the only way to see what is happening - where are you ? if you are in the Northern suburbs of Sydney I might be able to lend you a CRO

Regards Richard Freeman

Thks for the offer of the oscilloscope, that is really the way to do this, but I'm a long ways from Sidney unfortunately (virginia,usa). Trying to do this project on the cheap if I can help it. I think most of the issues I have are related to the use of high speed cmos chips on a bradboard with all that stray capacitance and long turning connecting wires. I've had some success so far using resistorcapacitor combos to make it work, I suspect alot of these problems will reduce somewhat when /if I move on to the pcb testing stage. Its been a long time since I learned all this stuff. The voltage levels you talked about do swing far above and below the thresholds in question but then that is when the dvm is already connected, but a schmitt trigger may be something I can try if I stop progressing altogether, will try to borrow a scope from somewhere. Thks for your interest

Unfortunately, Virginia is a long way from Sydney too.

Andy Wood snipped-for-privacy@trap.ozemail.com.au

If you ask nicely in sci.electronics.basics, you might get an old sub

20MHz scope for free, people toss this sort of stuff away quite regularly, and will happily donate to a beginner. Else you can pick one up for next to nothing on eBay.

Dave :)

Thks for the tip..

Good luck with your project but another thought occoured - it is usual when using a Photo transistor to receive some sort of signal to run the signal through a Bandpass (or at least high pass) Filter first - this should allow you to add some gain after the photo-tranny and increase its selectivity. The odd thing is though if you are placing a cap from the signal path to Earth then this is effectively a low pass filter ....

Regards Richard Freeman