Steampunk Electronics–Heartbeat

I’ve been playing around with making a pulsing LED that I will use in the body of the Steampunk gun. The LED will be mounted in the back of the gun and I will make a resin shell that will go around it … kinda like a dome on the back of the gun.

The circuit is basically a series of resisters, a couple of capacitors and a 2n6027 PUT (programmable unijunction transistor). The arrangement of resisters and capacitors shape the voltage through the circuit so that the first capacitor takes a short while to charge up, and then leak out. The result should be a gradual increase in the light emitted from the LED and then a slower decrease in the light.

I’ve seen some circuits on the interweb that use a 555 timer IC (integrated circuit) to do the switching from on to off, but this one from Charles Platt (Make: Electronics) is much more straight forward and should do what I need it to do. Plus … this circuit is cheaper than a circuit using a 555 timer.

I’m using a pin header for both the power connection as well as the leads for the LED so that I can have the LED on a flexible connection. I’m fitting the connecting wires with 2 pin DuPont female connectors so that I can easily connect the battery (9v) and the LED.

Parts:

• C1 – 100 µF electrolytic capacitor;
• C2 – 220 µF electrolytic capacitor;
• J1 – Generic female header – 4 pins;
• LED1 – pick whichever you like … I’m going to use a 5mm white ultra-bright 20000mcd that I picked up on eBay from (vendor bobpwaytoway);
• Q1 – PUT Transistor 2N6027;
• R1 – 33k Ω 1/4W 250V Through Hole Carbon Film Resistor;
• R2, R3, R4 – 1k Ω 1/4W Metal Film Resistors;
• R5 – 330 Ω 1/4 W Metal Film Resistor;
• VCC1 – 9V battery block;
• FR7 single sided copper clad board.

After jiggering around with the circuit for a while using Fritzing, the above PCB is the design that I’m most happy with.

The top two pin of J1 are connected to the battery. The bottom two are the LED.

I’m going to mount the LED in a ping-pong ball so that the light is more diffuse.

I’ll prototype the board this weekend and post any updates and photographs.

You can see that this is a very simple and small circuit, so it won’t take long to prototype or solder. I’ll make an intermediate prototype using perf-board so that I can see how the rats nest works out for me. The board is about 4.5 x 3 cm so the size should suit my needs too.