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.
Now that we have completed our visual check of the board and fixed the errors, it is time to apply power to the board.
Now that we have completed the power test, it is time to see if the board actually works.
In the following steps, we are simulating a zone that has been connected to the alarm system:
The following series of steps will test the output board, which the alarm system will use to talk to the outside world.
The following figure shows the test fixture that I built using a common protoboard.
From left to right, the output of the opto-isolator is connected to an LED. The emitter of the opto-isolator is connected to the ground terminal, while the collector is connected to the cathode of an LED. This LED is in turn connected to +12V through a 2.2K ohm resistor. When the opto-isolator is turned on, current flows from the collector to the emitter and the LED turns on. There are two identical circuits here; one for each output connector.
Connector J3 from the board is connected to 3.3V and four pull-down resistors. There is a 1K ohm resistor that is used to simulate the output of the BeagleBone. By connecting the orange wire to the various inputs, you can simulate a logical 1 on the input and turn on the opto-isolator. You will recall that we built a six-pin test connector in the previous chapter. It is this connector that you should use to connect the board you are testing to the protoboard. You can use any kind of 24AWG solid wire to connect J1 and J2 to the protoboard. SparkFun sells jumper packs for just this purpose.
For those of you who prefer schematics, the previous figure shows a schematic representation of the test fixture.
The 10K resistors are pull-downs that hold the input at logic 0. When you connect the 1K resistor to one of the pins of J3, you are applying logic 1 to the input. This simulates the output of the BeagleBone.
What we are about to do in the following tests is simulate the BeagleBone outputs without using an actual BeagleBone. In that way, we don't need any special software and there is no risk to our actual BeagleBone. The following steps show how we do it:
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