Cybug Scarab KitBy Ben Godfrey
Description: Cybug Scarab Kit
Assembly Time: 2 hours
Skill level: Advanced
The goal of this project is to build a light sensing robot capable of moving both forwards and backwards with antennae that help the robot steer clear of obstacles just like an actual insect.
Whenever I start a project, I like to look over the manual, and it is almost always possible to break the project into a series of steps. Below I describe some of my tips and tricks in building the Cybug Scarab Kit.
Step 1: ResistorsAlways measure the resistance of the resistors with a multimeter. Just because a resistor labels its value, do not trust that you have read it correctly. Trying to find a misplaced (or a bad) resistor is as difficult as trying to find a needle in a haystack.
Step 2: CapacitorsTwo of the capacitors are electrolytic, meaning they are polarized. The negative side (short lead) of the capacitor is marked while the positive side is seen on the silkscreen. Putting them in the wrong way produces some particularly acrid smoke when powered up and it is always a surefire way of showing that you have placed a capacitor in wrong.
Step 3: SemiconductorsThese parts include the diodes, LEDs and transistors. Always make sure you match the picture on the silkscreen to the part. If you think there might be a problem with any of the semiconductors, measure the voltage across the part and there should be:
• ~ 0.6 Volts across an LED or diode
• ~ 0.6 Volts across the base and emitter of the transistors
• Non-infinite resistance across the photocell in room light
When building this project, I actually had a bad LED, which I immediately noticed because it never turned on. Before putting diodes into the PC board, always check with a multimeter set in diode mode for a 0.6 Volt reading across the diode. Trying to remove parts from plated holes is very difficult and you may even remove the plating from the hole if you are not careful.
the Band on the Silkscreen
U2 (bottom) on the Silkscreen
Step 4: Integrated CircuitsAs a word of caution: Even if what you are building does not have IC sockets, always put them in. You do not want to have to remove a 16 pin IC when it starts smoking because you put it in the wrong way. In the picture above, one IC has the dot closest to the ‘+ -’ marking on the silkscreen (U2) while the other has it facing away from the 9 Volt marking (U1).
Step 5: General Construction• The hardest part of this entire project was breaking the PC board for the leg joints of the bug. If you have a razor blade or a sharp paring knife, saw off the joints next to D2 and S1 (D4 and R11 on the other side) first before applying pressure to each joint to break it. Then break the joint closest to C9 (or C5). Trying to break all the joints at once is very difficult.
• Do not try to hold the motor while soldering it. Instead, use a couple of pieces of masking tape to hold it in place while soldering.
• Save a couple of leads for the eye stalks of the robot (I forgot this and had to go fishing around in the garbage). To make them, I wrapped a lead around a pair of needle nose pliers and wrapped the excess around the straight part of the lead to create a loop.
Step 6: Final TweaksAmazingly, when I turned the Cybug Scarab on, it lit up and started walking around. However, there were a couple of tweaks that had to be made:
• One LED did not turn on, so it had to be replaced. Unfortunately, this meant unsoldering from a plated hole. If you have solder wick or a desoldering pump, you can try to use those, but I ended up being too aggressive and removed the plating from the hole. If you end up doing this, it is easy to see the traces on the silkscreen where the component is connected. (It is also good to verify this by looking at the circuit diagram provided in the manual or online). Then, it is a simple matter of soldering a jumper from the end of the component in the unplated hole to the end of the component that it should be connected to.
• The biggest problem I faced was when one of the motors fell off from the Scarab when the motor's leads disconnected from the motor itself. I fixed this by filling the sockets (where the leads were) with solder. Then I pushed the motor back into its original holes and held the soldering iron on one of the holes until I saw the solder start to flow. Since I was not sure if I had pushed the motor in correctly, I turned the Scarab on, and wiggled the motor back and forth until the motor started turning and soldered it in place. Finally, I covered the large middle hole and the PC board around it with super glue just to make sure it would not come out. This method was politically incorrect, but it worked.
Finally, I remembered to have fun!
Ben Godfrey is an electrical engineering student at the University of California, Davis. Ben has written iPhone applications and is a ham radio operator.