Hello everyone new on here
I'm the technical manager at Camera Obscura in Edinburgh
We recently had a piece of kit fail on us and I'm looking for a little help.
We have an exhibit that is ill the part that has failed is a timer circuit, Simply you press a button the small speaker beeps three times and there is a 5v trigger sent to a flash gun. I keep going round in circles on this as it's been the better part of 25 years since I did any hands on electronics. If anyone would like to assist with a circuit diagram or if any one would like to assist with the build please any help would be appreciated.

 

hi CO,
Welcome to AAC,
Do you have a diagram/photo of the existing electronic timer, we may be able to fix it. if not design a new one.
E

 

Thanks for the welcome
Hope this helps It was built in 2008 so the basics should be that same but it looks like two timer circuits?

 

hi,
It looks like simple timer, perhaps a 555 driving a counter.
Is it a beeper module or an actual small speaker.?
What are the timing intervals of the beeps.? eg: 1sec On, 1sec Off... *3
Where is the power supply located, ie: battery or mains.?

E

 

It was a small speaker but it's not essential a buzzer would do just as well. It was 3 seconds of a beep each second so Beep, one second pause, Beep, one second pause, Beep one second pause then trigger to the flash gun. I was thinking a 555 too..
Power supply was an off board transformer.

 

Please squint down in there and report all of the writing on each integrated circuit and transistor. My guess is that one of them says "555" and the other "4017", both with some extra letters.

Also, in what way is the circuit "ill"? No beeping, beeping but no flash, etc.
And, what tools do you have for diagnosis?

ak

 

A better picture, it just stopped doing anything.
When we opened it up the transistor was pretty warm so I replaced that however to no avail.

 

Well, the large IC is a PIC, a microprocessor. It is doing the switch interface and beep timing. The 555 could be the oscillator/driver for the speaker since it can source/sink 200 mA. Is that a miniature relay on the end? I guess that makes sense because it gives you a set of dry (fully isolated) contacts to talk to the camera without worrying about connecting grounds.

What you are calling a transistor might be a voltage regulator. What is its part number?

Overall, it seems to me that the circuit is more complex than it needs to be. If you are certain about your requirements, I don't think a programmable device is justified. For one thing, it makes the circuit impossible to debug without knowing the program code.

ak

 

I thought it was way over the top too.
Literally all the “exhibit” does is fire a flash as you stand in front of a photoluminescent wall leaving your shadow behind. The flash is a studio strobe flash so just needs a trigger to fire. The person using this presses a button then poses in front of the wall and the timer beeps then the flash fires.
So all it needs to do is recognise a button push then count down while beeping once per second, then trigger a 5v to the flash unit.

 

Can you confirm that the wires to the camera come from the relay?

What is the power source for the circuit?

Voltage
AC
DC

Photo of the power supply?
Part number on the large transistor-looking device?

ak

 

Can you confirm that the wires to the camera come from the relay?

What is the power source for the circuit?

Voltage
AC
DC

Photo of the power supply?
Part number on the large transistor-looking device?

ak

The wires go to a jack on the back of a studio flash (5v trigger) and the supply is a dc transformer but could be whatever is needed tbh

 

Trying not to be semantically picky, but here is no such thing as a DC transformer. So, what is the output of the power supply you have now? It is a clue to the circuit.

My guess is that it is 5 Vdc output, because the Tianbo CR5V relay and the PIC both take a 5 V power input. The relay coil draws 30 mA, so a CMOS output will need an external transistor to drive it.

Back to post #7, what is the "transistor" that is getting warm? An actual transistor, a voltage regulator, ... ? Nothing in the box should draw enough current to get warm.

ak

 

Trying not to be semantically picky, but here is no such thing as a DC transformer. So, what is the output of the power supply you have now? It is a clue to the circuit.

ak

ok it’s pedantic, but it is fed from the uk mains via an ac-dc PSU just now fairly sure it’s 5v output to a mini jack but could be as required for what I end up replacing this with.