SpudFiles

Don't need a o scope for these simple circuit's. Try and add indicator LED's where ever you can, test the transistor, test the opto isolator, and see if the flash circuit is working. You should have put it on a breadboard first.

Also, make sure the correct pins are connected, when you flip the board to solder, it will look different.

Hang in there Insomniac, I think you are getting close.

Measure the voltage across the 1uF cap (from the cap+ to circuit ground), it should be 9V. That cap is what supplies the energy to light up the LED in the MOC. The 9V battery can't do it directly since it is limited by the 1 Megaohm resistor. So, without the cap the LED can only get 9 microamps, not nearly enough to get it to light up much.

Try shorting across the right hand transistor in the schematic, from its collector to emitter. This should fire the MOC. Indeed, remove the transistor completely and replace with a switch. That switch should fire the MOC.

If the MOC won't fire this way then there is something wrong with the wiring to the MOC or the MOC itself. The LED in the MOC is polar, it must be wired in the proper direction. It must also have a current limiting resistor or the LED will be instantly fried. Usually, for a 9V battery about 300~500 ohms of resistance is required.

So, you might try just a 9V battery, a 300 to 500 ohm resistor and the MOC. Connecting the battery should fire the flash.

If that all seems OK then the problem is in the triggering circuitry.

Like someone said, remember that everything is upside down when viewed from the bottom of the circuit, and it is real easy to get the pinout on the transistors mixed up, indeed, transitor pins are not standarized in terms of which one is which.

If you've wired one of the transitors backwards then there is a good chance you cooked it, most transistors will only tolerate about 6V in the wrong direction. Your 9V battery will instantly cook most transistors if it is hooked up wrong.

EDIT: One more thing... are you sure the MIC is OK and that it is suitable for this application? There are a lot of different types of MICs and they are usually not swappable in a circuit. I suspect that this circuit is for an Electrek mic. Try shorting the 10uF cap near the MIC to the 9V, that should fire the circuit. (Or perhaps short it to ground).

EDITEDIT: Google for "Winscope". It is a O-scope program that uses a PCs soundcard. You can probe just about anywhere in your circuit without too much worry of frying the soundcard. Anywhere except the 300V of the photoflash

With the mic comment, Some MIC's have built in amplifiers, some need a external one.

I've tried shorting across both transistors from E to C (both one at a time and at the same time) and nothing. I may try putting two 220 ohm resistors in series connected to my 9V connected to one of the MOC's connected to the flash, to see if the MOC can indeed fire the flash. I tried replacing the MOC with a spare and it didn't work btw, so it's not just that particular MOC causing an issue. From the 1uF cap, the V difference between each lead on it is about 6 V, which drops rapidly when I attach the multimeter.

I tried two mics, both simple PC type mics. Somone in the comments reported success with a similar mic so I don't think that is the problem.

With this circuit we wired it up so that when you looked at it from the solder side, it matched the diagram. When you look at it from the componet side it's upside-down, but all the parts are connected correctly. We took our time and double checked each placement before we soldered. I'll go test with just a MOC now and see what happens. The pin next to the little round dimple is pin 1, correct? And it should be the positive lead of the LED, and the one beneath it be the negative?

Ok, I did some tests with the MOC.

Firstly, I ran leads from the pins that should be 1, 2, 4 and 6.

I ran the wires from 4 and 6 to the camera's trigger, and put 1 and 2 onto a 9v battery. I had two 1kohm resistors in parrallel to give about 500 ohms of resistance to the circuit so I wouldn't blow it up, and had pin 1 going to positive and pin 2 going to negative. The flash didn't fire. I tried a few times but it just wouldn't go off.

So I tried again, but instead of attaching the camera to 4 and 6 I attached my multimeter and told it to measure resistance. Resistance was off the scale when I had 1 and 2 not connected to anything (as it should be), but when I connected 1 and 2 to the battery in the same way as the last test, the resistance dropped to 7.4K ohms.

So, even when the moc fires there seems to be enough resistance that the flash can't discharge though the trigger transformer quick enough. Or the MOC isn't fully turning on and dropping it's resistance low enough.

EDIT: So I guess now all I need is a way to test whether the MOC is firing when it hears a noise in the real circuit (may make a little circuit with a LED and battery to test, I can see it flicker faster than my meter can read resistance), and if it IS firing, then I'll need to make a separate low-voltage trigger for the camera using an SCR, then attach that to this circuit.

Exactly how do you have the MOC wired to the flash board?

The MOC should not be controlling the 300V photocap, that won't do anything since 300V won't trigger the flash tube. The MOC should be connected across the flashboard's trigger contacts (the ones that'll read about 70V even though there is actually ~300V across them). Is that how you have it setup?

The reading of 7.4K ohm across the MOC's triac really doesn't mean anything, other than it is indeed switching on. Semiconductors don't generally obey Ohm's law which the meter relies on. The triac will have a volt or two voltage drop and nearly zero resistance beyond that. A typical DVM can't measure the reistance since it can't take that voltage drop into account.

Does you meter have a "diode test" setting? A diode test measures the voltage drop across a diode, which is typically in the range of 0.4 (small signal diodes) to 2V (high power high voltage diodes). The triac should look like a diode when it is triggered, with a voltage drop of a volt or so, and look like a very large resistance when it is not triggered. You can also use a 9V battery, 300Ohm resistor and LED for the MOC to control. When turned on you should be able to measure the volt or so voltage drop across the MOC's triac. If the MOC really does have 7.4K ohm resistance the LED won't light up since there is too much current limiting resistance in the circuit.

(LEDs typically drop ~1.4V and operate at about 20mA. A 9V battery in series with a resistance of R and assuming the MOC triac drops 1.5V means the resistor has to drop 9V-1.4V-1.5V=6.1V. The LED needs 20mA to operate so there must be 20mA through the resistor. Ohm's law on the resistor says 6.1V/20mA=305 Ohms resistance. Any resistor from 200 to 500 ohms should work.)

Yeah, of course I have it wired to the flash trigger wires. If I short out the jack I'm using to plug it in (or short out the 4 and 6 pin of the MOC ) it will fire.

I'll try the diode test later.


EDIT:

Ok, when my meter is on the diode symbol and I attach it to MOC, I get the 'off the scale' 1 on the screen. If I then trigger the MOC with the 9V battery and 500ohm resistor setup (two 1kohm resistors in parrallel) I get '916' on the screen of the meter, with no decimal places or anything.

Hmm... odd.. when I removed the battery it stayed that way..... then went back to the 'off scale' sign, and now the MOC won't trigger... Very strange.



When I attached an LED and 3V coin cell battery in series with the MOC's triac, triggering it wouldn't light the diode. When I just had the battery and the LED, it would light easily. So somthing in the MOC is amiss... causing too much resistance or somthing else like that. I am testing a different MOC (same model, 3021, but one of my spares) than the one in the circuit.

EDIT: Forgot to mention, I tried the diode test earlier, and got different results to the test I posted. It would be off the scale, but once triggered it would sit around 850 (I think thats the voltage drop in millivolts, or perhaps microvolts... Will have to check the manual). Anyway, what was happening was that when I disconnected the battery to un-trigger the MOC, the meter would jump up to somwhere over 900... add power, and it would drop down to 850ish again.


What would be a simple test (on one of my spare MOC's that hasn't seen the 300V of the trigger cap) that would verify it was working? I could try that, then connect it to the flash, then disconnect it and test again. This would let me see if the voltage or current that the trigger cap can deliver was damaging it.

Insomniac wrote: What would be a simple test (on one of my spare MOC's that hasn't seen the 300V of the trigger cap) that would verify it was working? I could try that, then connect it to the flash, then disconnect it and test again. This would let me see if the voltage or current that the trigger cap can deliver was damaging it.

The attached circuit should test the MOC.

I wonder if the problem is the leakage current of the triac? Diodes leak current even when they are "off" or reverse biased. IIRC, the leakage current is usually in the tens of microamps. The data sheet for the MOC3020 says the reverse current (I_R) is "0.05 to 100uA".

The charging circuit for the flash trigger is 300V through a 1 Meg (?) resistor so the charging current to the trigger cap is at most 300/1e6=300uA. Perhaps there is enough leakage through the triac so that the trigger cap isn't getting fully charged?

The circuit diagram you are working from is probably for a much more serious flash unit with a more powerful supply to charge the trigger cap. With the circuit all wired up do you get the same voltage across the trigger cap as you do with the photoflash board disconnected from the MOC?

Hmmm... I might go and buy some prototyping breadboard and then I'll test your circuit.

prototyping boards are very useful. Buy one with a power bus. Also get a jumper wire set, makes things much easier.

Hmm... bought a prototyping board/jumper wire kit, and have used a meter and jumper wires to work out how it's all arranged inside. Pretty simple once you get used to it. Tried that circuit you posted... and the LED didn't light when I closed the switch (the blue jumper at the top of the circuit is acting as a switch)

Wait a sec... while posting this I had a stroke of genious and remembered the two far-away pins are 1 and 3... not 1 and 2. Just moved a jumper wire one hole and it now works.

Now I know a brand new MOC works, I'm gonna switch it with one we had been using in our failed trigger. (Hah, I'm writing this as I go so It's like a running commantary )

Ok, did that... and my little yellow FLED is blinking happily away. So the MOC isn't being fried by my other circuit... yet the trigger circuit fails to work. Hmmmmm..... electronics is intreiguing and a bit frustrating.

Btw, here's a pic of my proto-board and the test circuit (note that in this pic I have the long red jumper going to the wrong leg on the MOC... I've fixed that)

Nice little board you have there. I've been through a few of those in my day... 8)

Thats a ugly board =p its all yellow...
For reference, all + on one side is connected (NOT connected to the other side positive), all minus, and each row of four is connected. Be carefull with components, everything from 555 to power IGBT's to resistor's have melted my board.

I think my board is a tad different from that... it is actually made of three seperate (both physically and electrically) parts... the main middle section, and the two 'power' bars (which are identical). The middle section has each row of 4 connected, with each row seperate from any other row.

However, all the negative's at the bottom are connected, but ARN"T connected to the negatives at the top (which are again, all connected to eachother)

Both positive rows are broken up so that you can have each section wired to a different supply voltage.


Btw the yellow tinge is a 'feature' to make your eyes hurt less when looking at it for hours on end.

OK!

Try this.

1. With the photoflash board disconnected from the MOC, charge up the flash board.
2. Measure the voltage across the flashboard's trigger contacts (should be the same as the voltage across the 0.022uF trigger cap). Probably reads about 70V with a DVM even though it is actually close to 300V.
3. Carefully connect the MOC to the flashboard trigger.
4. Monitor the voltage across the trigger (which is now the same as the MOC's triac pins).
5. If the voltage starts to drop then there is too much leakage through the MOC's triac, the trigger charging circuit can't keep up with it.

Just connecting the DVM (in voltage mode) across the trigger contacts is also probably enough to get the voltage to drop.

You could also hook the DVM up in series with the MOC and measure the current. Probably need a current range in the low microamps.

If there is too much current leaking through the MOC's triac then ....

A. You might try decreasing the resistance of the 1(?) Megaohm resistor that is between the big-ass cap and the trigger cap on the photoflash board. Perhaps a 500K or 200K resistor.

B. If the leakage through the MOC is too great and it prevents the trigger cap from charging, but if you can get the cap to charge and then connect the MOC and have enough energy in the trigger cap for long enough to get a shot, then you might put a switch in series with the MOC's triac. Switch it off when charging the photoboard then switch it on right before firing.

Now that you have the slick prototype board you might as well rebuild the trigger circuit on there until you get things figured out.