Saturday, June 9, 2012

Amp Hour Meter moves to protoboard

Our Amp / Watt Hour Meter (we need a snazzy name for it!) has moved from solderless breadboard to a more permanent protoboard. We have drilled holes all the way through the protoboard for the ring terminals to the load and it's power supply (the big holes in the current sense board), and installed screws with nuts to attach ring terminals. There are larger nuts between the current sensor board and the protoboard as spacers. Washers are installed under the screw heads, above the current sensor board, and above the screw terminals. This protoboard not only holds the current sensor, but also contains the voltage divider for voltage sensing. There are only 4 connections to the Arduino:

Analog out (current)
Analog out (voltage)

and 3 connections to Load / Power supply

Power supply GND (-)
Power Supply + (P+)
Load + (L+)

TCRT5000 IR Emitter/Sensor

I finished the carrier board for our tachometer project. This is simply the TCRT5000 IR emitter/sensor module, with the 150 ohm resistor for the IR LED, and the 10k ohm resistor for the phototransistor, as described in

I used a 3 pin header with the GVS pin standard as described in

The inexpensive breadboard from Radio Shack makes a great prototyping board when it's time to upgrade the project from a solderless breadboard. It gives the project some permanence. Solderless breadboards are good for temporary testing / design.


Sunday, June 3, 2012

Ground Voltage Signal Wiring Standard

The Gnd / Voltage / Signal (GVS) standard is very popular in the Arduino world, and consists of a 3 pin header, where Gnd and Signal are on the ends, and Voltage is the center pin. This helps by making cabling standardized, and makes it easier to plug new devices into your project.

The color code is black for Gnd, red for Voltage + , and typically brown or yellow for the Signal, although white is also used.

We use this standard with many of our sensor projects. There is a 4 wire version as well, G / V / S / S, for serial communications. The two signal wires may be yellow and white, yellow and brown, or some other combination, but ground will always be black, and voltage will be red.

Hardware Switch Debounce

We use a software debounce in many of our sketches. What's a debounce? A mechanical switch does not make a clean on/off transition, and if you are sampling fast enough, one switch depression could look like several to the Arduino. The most common method of resolving this is to check the switch twice, and if there is no change, then consider it a true trigger. This incurs delays, and messy code. A hardware debounce uses a R/C circuit (resistor / capacitor) to deliver a single shot. Thanks to Jeremy Blum, we are also using a inverting Schmitt Trigger to clean up the output for a nice precise square wave. The M74HC14 has 6 inverters on board, so you could build a shield or carrier board with 6 debounced switches for very little cost. Just need one M74HC14, six 10k Ohm resistors, six 10uf capacitors, and six momentary on button switches. The M74HC14 has a GND connection on Pin 7 and a +5vdc on Pin 14, not shown below. The carrier board would only need +5vdc, GND, and 6 outputs to the Arduino.

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