In the first article, I was talking about using the Charles Platt design for creating a pulsing LED using a 2N6027 PUT, a couple of resistors, a couple of capacitors and an LED.
Today, I took the schematic from Make: Electronics (by Charles Platt) and built it on a prototype board.
The first thing that I did was to transfer the resistors from the schematic onto the prototype board. It’s a simple design with not many components, so I decided to have the resistors spanning the separation channel in the middle, and then use jumper wires to connect them all.
Next, I put the capacitors in place along with the transistor and the LED.
Finally, I jumped the components so that they were connected according to the schematic.
I connected the battery (9V) to the board and waited … and waited. There was something wrong.
I needed to get out the multimeter and work out what was wrong.
I tested the battery … it was measuring 8.94V so that wasn’t the problem. Next I tested continuity on all of the jumpers … they were working fine.
Test the resistors, also OK. Interestingly, the resisters that I bought from eBay … all within the stated tolerance, so, Yay.
Test the capacitors … also fine.
I tested the LED and it was also peachy keen … so what had I done wrong?
I noticed that the prototype board power rails had a break in the middle and that I needed to jump between the gaps (d’oh!) I should have realised that this was the case, but then, this is the first time that I’ve used the prototype board in earnest.
After putting in the jumpers, I powered it up and … presto! it works just like is says on the box.
I’ve colour coded the jumpers so that I know what is going where.
White jumpers connect to a resistor, Green jumpers connect to a capacitor, Blue jumpers connect to the transistor, Yellow jumpers connect to the LED. Black and Red are Negative and Positive power respectively.
I’ve just been playing with the circuit a bit and I’ve decided that the timing for the LED was wrong. The LED flashed too quickly for my taste with a cycle of on-off in about 1 second. I’ve replaced the capacitors in the circuit. Now the capacitors are:
The on-off cycle is now about 2.5 seconds and much more pleasing for me.
Next, I’m going to transfer this to a perf board and put it in a project box. I think that this will work well for the Steam Punk prop. The prototype perf board will be larger than the one that I will use with a PCB, simply so that I have space to wire it. I will be using a standard copper padded perf board and the holes are all pre-drilled, so there won’t be much opportunity to compress the design. Also, because I will be using wire between the components rather than copper route, I will need some extra space for soldering and general jiggery pokery.
Anyway … it’s time to go and play with perf board and project boxes.
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