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Project Help and Ideas » I need some help on a circuit

November 12, 2012
by Pew446
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I've been playing around with this circuit for a while, and can't find out what is wrong with it for the life of me.

I found this schematic on Schematic

And I have been trying to create it myself. I ordered all the parts off TaydaElectronics, and created a circuit board: PCB

Here is my parts list:

NE555 IC 555 Timer DIP-8

10K OHM Trimpot Variable Resistor 6mm

180 OHM 1/4W 5% Carbon Film Resistor

470 OHM 1/4W 5% Carbon Film Resistor

560 OHM 1/4W 5% Carbon Film Resistor

1K OHM 1/4W 5% Carbon Film Resistor

BC557 Transistor PNP 45V 0.1A TO-92 BC557B-KEC/P

Infrared LED 940nm 5mm TSAL7400 (x2)

1N4148 Switching Signal Diode (x2)

10nF 0.01uF 100V 5% Mylar Film Capacitors (x2)

8 pin DIP IC Socket Adaptor Solder Type

Yet, it does absolutely nothing. I've checked that all the parts are in place correctly, but I have some confusions about the transistor. On the schematics, the arrow points towards the base. On the datasheet, it is on the opposite leg, pointing towards the base. Does this matter? Here is the datasheet.

I made a breadboard in hopes it was the circuit board at fault, but it doesn't work either. Here are a couple pictures, I tried to get angles so you can see all the connections.





Again, I can't figure out why it's not working. If you need more info, or have questions, please ask. Thanks.

November 12, 2012
by pcbolt
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Pew -

How do you know it's not working? Did you try substituting visible LED's in the circuit? Or did you try and use your remote at the same time as the jammer?

November 12, 2012
by Pew446
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Well I used my camera to look at the LEDs and saw no light. When I hook the leds up to my variable power supply, I can see the light just fine.

November 12, 2012
by Pew446
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I just substituted some red LEDs and saw no light. The battery is good, by the way.

November 12, 2012
by pcbolt
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Pew -

Your wiring looks correct. It looks like the transistor is right too. I think what I would do is use a multimeter to test for continuity at each of the 555 legs. Then check to see if you can light up an LED through the 180 ohm resistor by itself. If that works, try lighting the LED with the transistor in place and instead of putting the other end of the 560 ohm resistor to pin 3, try putting it to ground. Then check the resistance of the pot at different settings to make sure that is correct. There's always the "tear it apart and rebuild" solution, but I'd do that as a last resort. Oh and just double check if the caps are polarized. I don't think they are but I haven't used the mylar ones before.

Good luck, let us know how it turns out and who you're going to drive crazy with the jammer :-)

November 18, 2012
by Pew446
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I managed to get it working by just making a new board and rebuilding it, not sure what I did wrong in the first place. Probably blew a resistor or something. I'm actually going to be selling these in kits. My tech teacher buys electronic kits every semester for his classes, and he said if I can get a working kit for sale he'll start buying them from me. Here's my website.

It's a work in progress. I need to have a working kit by February, that's when he buys his next shipment. Currently my biggest problem is the etching quality, and the holes. The etching is done in vinegar and hydrogen peroxide, which not only takes a long time, but makes for pretty wiggly traces, sometimes cut in half. I think I'm going to switch to ferric chloride. I chose this method because it was cheap and non-toxic. Ferric chloride scares me a bit.

November 18, 2012
by Ralphxyz
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Why not get the boards made in China using Rick's fab house the prices for twenty boards are really reasonable and the quality is excellant!


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