In the previous chapter we built the hardware for our alarm system. Now it is time to test the hardware. We will do that by first testing it without the BeagleBone attached. The boards that we built have built-in test LEDs, which will allow us to test the hardware without running any software, or even connecting the hardware to a computer.
You will find this feature handy when you actually install the sensors. You can have a partner-walk-around trip sensors, and open and close windows and doors, all without running any software. Basically, if the zone LED goes on and off when you open and close an alarm circuit, your wiring is good.
In order to test the alarm system board, you will need the following two pieces of lab equipment:
- A variable dual power supply capable of supplying up to 15V and about 2 amps. The supply should also have current limiting.
- A multimeter capable of measuring up to about 15V DC supply with a milliamp scale as well.
Both of these are readily available on eBay and elsewhere. My local hardware store regularly sells multimeters for about $20.
If you don't have or can't afford a variable power supply, use AAA batteries in series to get yourself a 13.5V and a 3V supply. The batteries won't supply enough current to do any serious damage, in case of the 13.5V version.
A 13.5V DC supply consists of nine 1.5V batteries connected together in series.
A 3V DC supply is two AAA batteries connected in series. This will be used to simulate the 3.3V supply from the BeagleBone.
Before we actually power up the board for the first time, we need to do the following basic visual checks:
- Check if the diodes and transistors are installed properly.
- The band on the rectifier diodes should match the outline on the silkscreen.
- The case of the transistors and LEDs should match the pattern on the silkscreen.
- Check if pin 1 on the IC is in the correct position. (The IC hasn't been placed backwards!)
If all of these are checked, then you are ready to apply power to the board.
If everything appears to be correct, then you are ready to proceed to the next step.