Adding an Auto-Calibrate button - [R5 Rev-1]

The Auto-cal procedure is described here in the main 2D0 page. A button, resistor and capacitor must be added to the unit. The actual schematic is shown at right with a 22k pull-up resistor (any value from 10 k to 100k should work fine) and debounce capacitor (10 nF to 100 nF or 0.01 uF to 0.1 uF). The actual button (PB) goes across the debounce capacitor. Also shown is an optional zener diode (only needed for very long cable runs to the button) and is designed to prevent spikes getting into the button circuitry.

The image at left shows one way of performing the changes to an existing 2D0 unit. Click on the image for an enlarge popup showing a view of the added resistor and capacitor.

Note the slightly different orientation of the components in the popup. The resistor goes between pins 14 and 16 of U4. The capacitor between pins 14 and a close by GND point. The press button (not shown) goes from pin 14 to the GND point. The press button is a normally open, or ON while pressed (ie. not momentary action) switch and any low voltage switch should work.

Don't forget that firmware 0652 or later is required to enable Auto-cal mode, and that the operation of the button is described here.