Arduino Monitor/Tester

The reason for this little gadget is that although it is possible to monitor a lot of things through the serial interface, there is still nothing as good as seeing the actual signals on a β€œlamp” display. Many years of experience with electronics and automation have tought me that it is a very bad idea to monitor something through the same channel that you suspect to be faulty. In my development of the Purix controller I have had invaluable help of my first little Arduino test-shield with LEDs on all I/O’s in use, and also of the LEDs that we put on the prototype controllers. . . The features are the following:

  • One LED for every single input or output
  • Can be used with Due (target), Mega, Uno, etc.
  • Fit with my Mega Shield, a universal I/O board
  • Power taken from Arduino 5V output
  • Selectable 5V-3V input modes (for Due operation)
  • Voltage for steppermotor output can be selected between 5V and Vin
  • Monitor-load-resistance on any pin is 10 kohm or higher
  • LED intensity is proportional to pin voltage or duty cycle
  • IC-sockets and Arduino pins are all gold plated πŸ™‚
  • Built-in inputs and outputs for testing new ideas:
    • One pushbutton (P) digital input
    • One toggle switch (T) digital input
    • Two potentiometer (1, 2) analog inputs
    • 4 outputs also connected to HEX-display (eg.: for program state indication)
    • Very small moving coil voltmeter on PWM output (from old tape-recorder :-))
    • Piezo loudspeaker on PWM output
    • 4 open-drain MOSFET outputs, incl. flyback diodes (for small stepper)
    • One opto-isolated digital input
    • One opto-isolated digital output (not for 230 VAC)
    • One direct analog input via miniature LEMO coax connector
    • One direct digital I/O/PWM via miniature LEMO coax connector
    • One reed-relay (no coil) to digital input
    • One mercury shake alarm to digital input
    • One TMP36 temperature sensor to analog input
    • One electret-microphone to analog input via op-amp (gain 100)
    • One NTC, linearized, to analog input
    • One LDR to analog input
  • All inputs and outputs can be made passive to enable inputs from other external sources
  • LED’s grouped in 16 for analog I/O, 14 for digital I/O/PWM, 8 for digital I/O/Tx/Rx and 32 digital I/O. In total 70 LEDs
  • All LEDs are very high efficiency white SMD types, with coloured film on top according to the group
  • The LEDs cathode reference is adjusted down to approx. -2V: LED will light up when pin voltage goes positive

The cathode reference is divided into one for analog and one for digital, and both can be adjusted . The small white LEDs from Osram (DURIS E3, type InGaN) are fabulous. In the photo above you can see how I mounted them. With a current of only 0.5 mA they will produce more that enough light for the monitor purpose. This means that I only have to load the inputs and outputs with 10 kohm.

As much as possible information is written on the front panel. This is a bit tricky, since some of the pins assignment differ between Mega and Due

The front panel consists of a sandwich of two pieces of transparent acrylic, a little longer than a MEGA board, and the same width. Between the acrylic pieces is a layer of semi transparent PCB-layout-“paper” (2,54 mm module), the type we used many years ago for taping up PCB lay-outs. The text is made with so-called “Letraset” letters that you transfer by rubbing each one of from a sheet with a collection of letters. All in all very old-school πŸ™‚

This is how the front panel looks now, with all indicating text and numbers. The thing on the left side is the shake-contact:


Below you can see the backside of the Monitor/Tester and all the pins that will go into headers on Arduino Mega/Due. You can also spot the jumpers for disconnecting all built-in analog inputs, and the selector for 5V-3.3V. A small piece of insulating film is placed where there is a risk that the large USB-connector (Uno/Mega) will touch. At the bottom of the picture you see the piezo-speaker, electret-microphone and two Lemo connectors:


Below you can see the separate compartment with the two LEMO connectors, TMP36 and NTC temperature sensors, and a blue LED indicator for 5V:


Click here to see the .pdf schematic: Monitor-Tester