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Build Instructions, Page 2 / 6

Step 2: Power Supply

The next step is to verify that the presoldered power supply functions correctly. To do this, we have to first attach the battery holder to the PCB. This component is polarized, which means that it matters which wire goes into which hole. In the bottom right corner, there is a designator of BT1. Next to one of these holes, there is a +. The red wire goes to there, and the black wire goes to the other hole. There are two strain relief holes. First, put the wires through the respective holes from underneath the PCB, and then poke the wires through their holes from the top. Now, flip the board over, and solder the two wires in.

Location of battery connectionsStrain relief holes

Use your soldering iron to heat up the wire sticking through and the ring around the hole at the same time. Push a little bit of solder on the ring. The solder should melt and flow around the hole. If you’re having trouble, make sure the tip of your iron is tinned and shiny. Remember to heat up both the wire and pad, and you don’t need to apply a lot of solder. Don’t try to use the iron like a paintbrush. You can review the soldering comic below.

Soldering comicFlip the board over

Be very careful, as a short here can be catastrophic. To check for problems, use a multimeter to measure the resistance between the two indicated solder points. The resistance should be very high (in the megaohm range) or else display an error. A low value means there is a short, and this needs to be cleaned up. In the picture below, our multimeter is measuring 22.11 megaohms, a very large value, meaning there are no shorts in the circuit.

Location of test pointsMeasuring resistance between power and ground

If the resistance is high (or so high it displays an error), insert the batteries. The flat end of the battery goes on the spring part of the holder. There is also a diagram on the inside of the battery holder. Use the multimeter to measure the DC voltage between the same two test points. It should be around 5 volts. When we tried it, our multimeter displayed 5.14 Volts, a good value to see. The voltage shouldn’t exceed 5.2 volts or be less than 4.8 volts.

Location of battery connectionsStrain relief holes

Before you continue with the next step, remember to remove the batteries.

Step 3: Sockets

The next step is to solder the sockets to the board. These hold the chips to the PCB, and allow us to remove the chip if needed. Insert the sockets into their proper areas on the board, labeled U2 and U3. There is a notch in one end of each socket that should line up with the notch in the drawing on the PCB.

Notches in drawing on PCBLocation of chip sockets

It usually helps to bend one of the legs to keep the socket in place while soldering. Take care to ensure that the socket is flush against the PCB while soldering, because it can be difficult to insert a chip into a crooked socket. Flip the board over, solder one leg, and then flip the board back. If the socket isn’t pressed up against the board, reheat the connection while pressing the socket to the board. Finish soldering the rest of the connections. Do the same for the other socket.

Solder chip in placeBending pins to keep socket in place

There are a lot of connections here! If the solder starts to act like putty, or the soldering starts to get more difficult, your iron is likely too cold. Take a little break and let the iron heat back up.

When you’re all finished, be sure to visually check for shorts between pins.