When developing an embedded application using analog sensor inputs, testing at specific sensor levels can be difficult.  For example, in my icemaker controller project, actions need to occur at certain water levels.  Using the actual sensor and a reservoir is time consuming, requiring filling and pumping out water to check sensor points.

Fortunately, simulating sensor operation is easy.  Many sensors, including my pressure sensor, output a 0 - 5v signal proportional to the input parameter.  A potentiometer (variable resistor) can easily simulate the sensor signal.

The schematic of a simple pot circuit is shown to the left.  End ends of the pot's resistive element are connected to ground and 5 volts.  The ADC input is connected to the pot's wiper which is a sliding contact along the resistive element.  The circuit acts like a voltage divider.  If the wiper is positioned near the ground terminal, the output voltage approaches zero.  As the pot's knob is turned, and the wiper movers towards the 5v input, the wiper terminal will be at a higher voltage.

Simulating a range of sensor values is as simple as turning the knob.

I recently had use for the simple signal generatorI described before for testing out some piezo buzzers I got for next to nothing.  I reloaded the code onto a TAP-28 board I had handy, made the connections and was quickly rewarded with some noise.

Since I find this really useful to have around, I decided to dedicate a TAP-28 board to the task and mounted it in an enclosure.  The the same time, I wrote a simple Windows (sorry Linux guys) application to control the signal generator.  No more button pressing and terminal emulator.  Just enter the desired frequency and duty cycle and away it goes.  Very handy.

The full details including a schematic diagram, Swordfish Basic source and compiled files and the Windows application can be found on the ThrowAwayPIC site.

Header pins are ubiquitous on dev boards.  Jumpers can be used to make connections during tests and code development but real-world applications need reliable connections.  Connectors for single row headers have always been a problem for me, but I've come up with a method to achieve reliable results.

Connectors for single row headers are pretty common.  You've probably used them for ISCP and seen them used for connections inside personal computers.

I had a couple of issues when using David Barkers module NMEA.bas on my Big GPS Clock project. In particular, variables were being corrupted making the program very unstable.

I'm not familiar with Davids programming approach, so I went on to create my own NMEA parser.

I'm working on a control system that will have several relays, a bunch of LEDs and a number of switches.  I was rapidly running out of port pins on a TAP-28 board to handle all the desired I/O.  Possible solutions included adding an I2C port expander such as the Microchip 23018, but this was an additional complexity to the already-expanding project.