Chapter 5. Testing the Hardware

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.

The test equipment

In order to test the alarm system board, you will need the following two pieces of lab equipment:

1. A variable dual power supply capable of supplying up to 15V and about 2 amps. The supply should also have current limiting.

2. 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.

Visual check

Before we actually power up the board for the first time, we need to do the following basic visual checks:

1. Check...

The zone input board

The following series of steps will test the zone board, which the alarm system will use to talk to detect changes in the outside world.

Power check

Now that we have completed our visual check of the board and fixed the errors, it is time to apply power to the board.

1. Apply 13.5V DC supply to either J1 or J2 of the board.

2. Connect the negative lead of the multimeter to pin 2 of either J1 or J2.

3. Measure the voltage at the anode (end without the stripe) of D4 or D5, depending on which connector you chose.

4. Make a note of this voltage.

5. Measure the voltage at the cathode (stripe) end of the diode. The voltage should be about 0.7V less than the voltage on the anode. (This is because there is about a 0.7V across the PN junction of most rectifier diodes.)

6. Apply 3.3V (or 3V if you are using batteries) to pins 1 and 6 of J6. Be CAREFUL because there is no polarity protection on this connector. Pin 1 is the positive terminal and pin 6 is the negative or the ground terminal.

7. You should measure...

Summary

In this chapter we tested the hardware that we built in the previous chapters. If you like, you can use the zone-testing portion of this chapter to test your actual installation wiring. Remember that you do not need the BeagleBone to test your wiring. That's what the LEDs are for.

In the next chapter we will learn how to use any unused outputs on the alarm system to control other things such as pumps and sprinklers.