What is the circuit meant to be and for what purpose???dsb_mac said:Hi I'm trying to build a simple circuit but my physics is shaky. Could someone be kind enough to take a look at what I've done and notice any rookie mistakes? Thanks! The top side is positive.
This is trigger for a camera flash unit. It's suppose to fire my flash unit when the infrared sensor gets interrupted. I don't know if I'm building it right. In any case nothing fired.The Bob said:What is the circuit meant to be and for what purpose???
The Bob (2004 ©)
oh i think they're locked down or sumpthin. I've never posted here before (I mainliy read the posts)christinono said:i would help, but can't open the attachments. They are not working.
To have an adjustable delay would be nice but I don't think that's part of the design. If it fired instantly would be acceptable. Pin 8 on the diagram is connected to the positive from what I can tell. The phototransistor (infrared detector) is diagrammed to be connected to pin6 i think. Thanks for looking.The Bob said:What time delay are you looking for between using the unit and it flashing??? (I ask because you are using a 555 timer circuit)
Sorry but this circuit layout is not familiar to me (some of the symbols do not look like the ones I use). Is the transitor connected to Pin 8 of the IC??? (Unless it is not a transistor and your use of symbols is different to the ones I use)
The Bob (2004 ©)
i'll have to review the connections of the 555 timer, but the gist of this circuit is that while the beam from the LED shines on the phototransistor, the phototransistor acts like a lower resistance than when there's no light hitting it. the phototransistor and the variable resistor (the 10k with the arrow through it) form a voltage divider; light shining on the PT makes pin 6 of the 555 go up in voltage; cutting off the light makes that voltage drop.dsb_mac said:To have an adjustable delay would be nice but I don't think that's part of the design. If it fired instantly would be acceptable. Pin 8 on the diagram is connected to the positive from what I can tell. The phototransistor (infrared detector) is diagrammed to be connected to pin6 i think. Thanks for looking.
that's right I have an external flash that has an adapter to trigger it. I output wires from the scr to the adapter.the SCR would probably be connected (the two "output" arrow lines) to the input or remote trigger socket of your strobe, and by that i infer you mean "photoflash" unit, because those two connections alone won't fire a strobe lamp alone... many more components are needed to do that! :)
For now I'm using a sepearte tv remote control as the LED. I don't know what it means to connect to ground. When I connect between pin3 and negative I do get a voltage reading of 1.22. Then when I use a seperate remote control and press a button I get around 1.55. The 9v battery is 7.55.with light shining from the LED to the PhotoTransistor, measure the voltage from pin 6 of the 555 to ground. cut off the light between the LED and the PT and see if the voltage changes. if it doesn't, the adjustable resistor may be set to too low of a resistance, or the LED or PT may be defective.
When I do that I get an initial reading of 6 (remote on) to 6.5(no remote).if that seems to be working right, interrupt the light again and see if there's a short jump in the voltage from pin 3 of the 555 to ground.
I have no access to an oscilloscope but it seems to be working as per your description.if it's too short of a pulse to see on the meter, it gets trickier. a short pulse may only be visible if you can hook an oscilloscope to those pins and trigger the 'scope off pin 6...
between pin3 and the gate on my first attemt i get 6.11 (no remote) 5.55 (with remote).next, the SCR may be defective, or it may not be getting enough current through the 10k fixed resistor between pin 3 and the SCR's gate connection.
trying a 5k resistor may help, or again, look at the SCR's gate with the 'scope, too. you should see a pulse at the gate, but it will not be much more than .5-.8 volts or so, while the pulse at pin 6 could be much higher.
i know that if i disconnect the leads to my flash and then touch them together it will fire.finally, your strobe may not be the kind that is triggered by this kind of circuit. this circuit will trigger a photoflash that's set off by shorting the input pins (that's what the SCR does in this circuit, effectively.) or, ...... well, let me know if any of these suggestions work, first....
"ground" in the circuit, as i recall, is the negative side of the battery....dsb_mac said:ok slight problem which i'm sure there's a simple solution. The circuit works sometimes. What I means is that when it works it will consistently work firing everytime but sometimes if turn off the circuit and come back to it it won't fire at all. Is this related to grounding?? I'll give an example one time it wasn't working so I did some testing with the multimeter. I touched the positive on pin3 and the negative to negative then all of a sudden it started working. Further experimentation shows that sometimes it fires when I take measurements from pin3 to the gate sometimes from pin3 to ground and sometimes pin3 to positive. It keeps moving around. How do I fix this?
running a wire directly from pin 3 to the gate of the scr will make the output of the 555 think it's driving pretty much a short circuit (the gate can't go much above .6v, no matter what the 555 tries to do), so having some resistor there is a good idea. if you're running about 9 volts into the 555, and for rough numbers, you want to drive, say, 20mA into the gate of the scr, a resistor in the 400-500-ohm range should work fine.dsb_mac said:Taking the resistor to pin3 was a bad idea. It worked for the half dead 9v I was using. But after I switched to a new one it heated up the timer chip really quickly. I did try adding a resistor to the gate but it didn't seem to solve the problem.