Kit Components:
1) 555 Timer
1) 8 pin IC Socket
1) 100 uF Electrolytic Capacitor
1) IRF 510 Transistor
1) 1N914 Diode
1) Variable Resistor
1) .01 uF Ceramic Capacitor
2) Terminal Blocks
1) PC Board
Take a look at the images at the top of the page, use them as a reference as you assemble the timer. To the right is the board with the parts laid out. It's probably easiest to start with the small components first. Make sure you use a low watt (such as a 15 watt) pencil tip soldering iron. Preheat the soldering iron and clean and tin the tip with solder.
Clean the copper trace side of the PCB with alcohol before starting, then allow to dry.
All parts are inserted from the top side (no copper traces). Insert the 8 pin IC socket into the holes first, it can only fit two ways and it doesn't matter which end it up, then solder each of the pins to the PCB pads on the back side. Use solder sparingly, but make sure each solder joint adheres to both the pin on the socket and the PC board. If you get a solder bridge between two pads, clean your soldering iron tip and try to heat one pad and draw the solder from between the pads.
Next we will insert the 1N914 diode, it goes in the two holes to the top left of the IC socket (pin2). Look at the diode carefully, you will see a black band on one end. This black band goes towards the IC socket in the center of the board. The nonbanded side goes in the hole towards the outside of the PCB. Solder the diode to the pads on the back side and clip off the excess wire.
Now we'll insert the .01 uF capacitor. It's not polarity sensitive, so the leads can go in either hole. It is located at the bottom right of the IC socket (pin5). Solder the leads to the pads and clip off the excess.
The 100 uF electrolytic capacitor goes to top right of the IC socket (pin 8), it is polarity sensitive, so insert it into the PCB with the negative side towards the outside, away from the IC socket. The capacitor is marked on the negative side with a stripe and a - mark in the stripe on the side.
Now solder in the variable resistor, also called a pot (potentiometer), it only goes in one way, just solder up all three pads on the back side of the board.
Now slide the two terminal blocks together, using the little dove tail joint on the side to join them. The holes are aligned so you can add a third terminal block for a break wire to start the timer. Or, you can just solder your break wire leads into the holes if you use them. Insert the joined terminal blocks in the left four holes, leaving the far right two holes open (for break wire). Make sure the openings on the side face up, or out, so you can connect your power and igniter wires. Now solder up the terminals on the back side pads.
The last component to solder in is the IRF 510 transistor. It goes in the last three holes just beneath the terminal blocks. Look at the photo above, the transistor has a metal flat side, and a plastic protruding side. Install the transistor with the flat metal side towards the terminal blocks. Solder the three transistor leads to the pads, cut off the excess length.
That's it for soldering, you can now clean up the back side of the board with a Q-tip and some alcohol. Some people like to coat the bottom of the PC board with a sealer, but if you ever need to work on it that makes it harder. Also, I wouldn't seal the back of the board until the timer has been tested. Keep in mind too, you may want to solder leads to the break wire holes.
Make one last check that you have no solder bridges where they shouldn't be. A magnifying glass really helps. Also check there are no bad solder joints, and no breaks in the copper traces. You can repair broken traces by soldering some 24 gauge solid copper wire where the trace is broken. Use the diagram at the top of this page to check the traces.
Looking at the timer from the top side (component side) with the terminal blocks up (as in the picture), the left two terminal blocks are for connecting the igniter leads, for an igniter it doesn't matter which lead goes where. The next two terminal blocks are for power, I pretty much always use a 9 volt battery, but you could use any power source from 9 to 15 volts. On the power terminal block the left or connector is for negative, the right connector for positive. Make sure they are labeled on the top side of the board so no mistakes are made when hooking things up.
The last thing to do, is to insert the 555 timer IC into the socket. You will have to bends the leads on the timer inward just a little to get them into the socket. I usually push one side of 4 leads on a flat surface slightly, then do the other side. The timer has a small dot next to pin one on the chip. That dot should go to the upper left, closest to the IRF 510 transistor.
Turning the pot clockwise will reduce the time, counter clockwise increases the time. Use a small lamp to test the timer, hook up a DC bulb to the igniter terminal blocks, and apply power to the timer. The timer can be set for 0 seconds to about 60 seconds. If you are careful in turning the pot only a small amount, you can generally get within .5 second accuracy.
If it doesn't work, check to make sure all the components are in the proper orientation. Check again for solder bridges, bad solder joints, or broken traces. The most likely component to fail is the IRF 510 transistor, if you have a voltmeter, you can check on pin three of the 555 IC, if the voltage goes high after the timer times out but the bulb doesn't light, the transistor is likely bad and should be replaced.
The transistor is rated at over 5 amps, and should fire any e-match on the market. I use homemade e-matches with 40 gauge nichrome wire that fire under 1 amp. I've been making and flying this timer for a few years now, it has proven to be rugged and the most dependable deployment device I've used.
There are a number of ways to start the timer. Keep in mind, as soon as power is supplied to the timer the countdown starts! So you can put a switch in line with a battery wire that closes when the rocket leaves the pad.
One neat way I found to do this was using a magnetic switch. While on the pad I used a magnet to next to the rocket where a normally closed magnetic switch was used. When the rocket left the pad and moved away from the magnet, the switch closed and started the timer. But you need a way to make sure the magnet is keeping the switch open, so I put a piezo buzzer between the battery leads after the magnetic switch. If the buzzer sounded, the circuit was timing and the magnet wasn't in proper position.
Perhaps the simplest way to start the timer is to use pull or break wires. What the break wire does, is when the break wire is hooked up and not broken, battery power is supplied to the negative side 100 uF capacitor, that prevents the timing from starting. So when a wire is run outside the rocket it forms a loop, when the loop is intact the timer won't start timing out. When the loop is broken, the timer starts. You can break the loop with a jumper wire and alligator clips, just tie or tape the jumper wire to the pad so when the rocket launches, the jumper wire stays on the pad, breaks the loop and the timer starts. If you use bare wire ends on the rocket, make sure they can't touch each other while in flight or the timing will start over again, not good. I offset the bare ends of the wire and inch or so, so they can't touch in flight.
Or, you can run the wire loop to a couple of small bolts or screws on the outside of the rocket. Again, using a jumper wire tied to the pad and clipped to the bolts. I would recommend using a main power switch in the battery power wire if you use the break wire, it's safer, and it keeps power consumption down until the last minutes before flight.