Emulator to replace both Intersil CA3161(E)/CA3162(E) using Arduino on bare ATmega

This Arduino sketch emulates both Intersil CA3161 and CA3162 (also NTE2054/NTE2032, ECG2054/ECG2032 ) used in many old device as a simple three digit voltmeter. It's written to run on bare ATmega88 or ATmega328 MCU, but can be easily ported to other Arduinos/MCUs.

Differences from the original CA2162(E):

• Emulator don't have differential input at this time and accepts only positive voltage as input, i.e. works only in configurations where CA3162E pin 10 is connected to ground.
• Zero and gain ajustment can be done only calibrated using the serial interface (9600bps 8n1)
• No hold mode, no fast mode.
• ADC resolution depends on the reference voltage used. In case of ATmega8 internal AREF (very inaccurate) it will be 3mV (or ~3 degrees of Celsius for SL-30).

Emulator requires minimum external components:

• Decoupling ATmega VCC and AREF pins to GND via 0.1uF ceramic caps is required.
• To be interfaced with the three BJT PNP transistors based digit drivers, it needs ~ 1K resistors in transistor base lines.
• It's recommended to connect RESET pin to VCC using a 10K resistor.
• (OPTIONAL) You could use an external voltage reference to increment the ADC precision, like the LM4040 voltage reference diode.

Calibration

To calibrate the emulator by voltage:

• Connect Arduino serial interface and use the command STATUS to get the uncalibrate voltage values.

• Connect your voltmeter to Arduino A0 pin (PC0 pin of ATmega, pin 23 on DIP28);

• Write down both values: the uncalibrate value and the one displayed on the voltmeter display;

• Repeat previous step 2-3 times, at different input values. See the table below for example:

  Display	Voltmeter, mV
  83	100
  184	203
  307	329
  589	620

• Find linear approximation for this data. You could use Wolframalpha to calculate zero and gain by entering the data like this: linear fit {83, 100}, {184, 203}, {307, 329}, {589, 620}. You will get an expression like this: 1.02812 x + 14.0734

• Use the multiplier from that expression and use the command CALIB to set both the values:

  CALIB 1.02812 14.0734

• If the value displayed on the three segment is correct, save the calibration values in the eeprom, using the command STORE

External useful informations

• CA3162 datasheet
• CA3161 datasheet
• Using ATmega8 with internal 8MHz oscillator as minimal Arduino tutorial and another one.