A possible decimal digit dvm?

Question

I would like to build a 3x10 decimal digit dvm for an edge lit numerical display. The nearest schematic that I can find is using a CA3162E / LM74LS147 which can be found at:

http://www.seekic.com/circuit_diagram/Measuring_and_Test_Circuit/DIGTAL_LED_VOLTMETER.html

A copy of the diagram at the above URL:

However, the CA3162E is difficult or expensive to obtain. The output leds are multplexed similar to a 3 digit, seven segment dvm driven by a PIC16F676 at http://www.circuitvalley.com/2012/02/30-volts-panel-volt-meter-pic.html

Is there a more modern circuit or a MCU replacement available or is there is there a MCU that can be configured as a BCD driver to drive an LM74LS147 or an MCU that can be configured for decimal output? Many thanks in advance.

Answer 1

There are several methods that you can use. Some methods are easier than other but all are inexpensive.

The most obvious method is to use a small microcontroller for each digit. Something like a PIC16F676 (14 pins) gives you 11- I/O and 1- Input only pin. There are 18 pin packages available that give you more pins but you really need only 11 or 12 pins.

A less obvious method is to use a single 4017 decade counter chip for each digit. You would drive the clock and reset lines of each digit from your controller - the reset line can be common to all digits and the clock line for each digit is simply pulsed to advance the counter to the correct digit.

4017 chips are darned inexpensive. They have an additional advantage that they can operate at higher supply voltages if you are using LEDs that have a high threshold voltage. You would need level translation for each of the 4 control lines (3- clk, 1- reset) but that is easy: a single small MOSFET & one resistor per control line.