Nuts and Volts - September 2016

The blue wire just creates a common ground between the Amigo and the nine volt battery.

Adiós Amigo(s)

That completes this introduction about extending your Amigo to the world outside the circuit board. With two Color BASIC commands and some simple hardware, you can greatly expand the fun (and learning!) you and your student can have with your Amigo.

Some things to remember:

A=INA[x] converts the voltage level on pin x to a 1 or 0 logic level in variable A. OUTA[x]=1 places 3. 3 VDC on pin x; OUTA[x]=0 grounds pin x to 0 VDC.

Always use a current-limiting resistor between the I/O pin and any circuit using a voltage source other than the 3. 3 VDC from your Amigo.

When using a transistor as a computer-controlled switch, don’t forget the bias resistor between the transistor and the I/O pin. If you don’t have the specs for your transistor, check the Parallax forums, or do a quick Internet search for images associated with “I/O pin <your transistor here>.” Consider a separate power source for motors or other beefy computer-controlled loads. Don’t forget the snubber diode if you’re controlling a motor!

Of the 16 I/O pins brought out to J8, P0-P4 are used to interface the Prop chip with the Amigo SRAM and SD card, but are still available for use after considering that constraint. Pins P5-P15 have no assigned duties and are exclusively available for your use with the Experimenter’s Section.

I hope these simple computer-controlled hardware circuits will bring you some smiles, and will fire up your imagination for cool things you can do together with a student and the Amigo. Future Nuts & Volts articles will discuss how your Amigo can measure resistance, hack an RC toy car, and some other fun hardware projects. Until then, be well! NV

Perhaps the easiest way to build your own Amigo is from the kit available from the Nuts & Volts webstore which provides everything you need, including the circuit board, all components (including an EEPROM pre-loaded with Color BASIC), and a 2 GB SD card with sample programs. However, if you already have a Propeller board with connectors for a PS/2 keyboard, VGA monitor, and 2 GB SD card, you can “roll your own” Amigo by downloading the Color BASIC source from the article link, updating the I/O pin assignments to match your hardware, and then loading the compiled Color BASIC binary to the EEPROM on your board.

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