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Build Instructions, Page 3 / 5

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Step 4: Transistors

Next, insert and solder the transistors. They are labeled Q1, Q2 and Q3 on the board. The legs need to be spread a little to fit into the board. The orientation matters, so make sure to follow the white drawing on the board. Make sure the flat side of the black transistor package is facing the seven segment display, aligned with the red line in the photo below.

Installed TransistorsAlign the flat sides

Flip the board over and solder all nine transistor leads. Trim the excess leads with your diagnonal pliers. Be sure that the leads don’ fly off and hit anybody! It might be a good idea to wear safety glasses or goggles, or at least hold your hand over the PCB to prevent the trimmed leads from flying all over te place.

Trim the excess leadsSolder the transistor leads


Step 5: Ceramic Capacitor

Insert and solder the ceramic capacitor, labeled C2 on the PCB. It isn’t polarized, so it can go in either way. Bend the leads a little bit so it doesn’ fall out when you flip the board over to solder the leads. As usual, trim the leads after soldering.

Installed Ceramic CapacitorLocation of C2


Step 6: Chip Socket

Insert the socket into the board. The footprint on the board is labeled U1. There is a notch in one end of the socket that should line up with the notch in the drawing on the PCB, next to the ceramic capacitor (C2) that was just installed. It usually helps to bend a couple 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. Like the seven segment displays, you might want to solder only one pin at first, and then check the alignment. If the socket is crooked, you can melt that pin’s solder and push the socket into place. Once it is aligned, solder the rest of the socket’s pins.

Bend two pins to hold the socket in placeInstall the chip socket


Step 7: Resistor and Power Protection Diode

Bend the resistor as shown and place it on the board. It belongs just above the push buttons, and is labeled R1. This part isn’t polarized so it can be installed either way. Insert it through the holes in the PCB and bend the leads outwards slightly to hold it in place. Solder it down and trim the legs.

Installed Resistor R1Bend resistor R1

Bend the much thicker leads of the power protection diode in the same was as you did the resistor. This diode is labeled D1 and is at the bottom of the board underneath the chip socket. Unlike the resistor, this diode is polarized and can only be inserted a certain way. Align the thick silver stripe on the diode with the thick white line on the PCB, on the left side of the diode footprint, the square pad. It should look like the image below. Push the diode flat agains the PCB and bend the leads out slightly. Solder and trim the leads. When you’re finished with this step, the resistor and diode should both be flat against the PCB.

Installed resistor and diodeBend and install the power protection diode