Digital Ammeter

This circuit is made up of two integrated circuits: an analogue to digital converter (CA3162), and a decoder of seven segments (CA3161).
The power supply is 5 volts c.c. and features only two settings, R2 - 47k used to initiate the displays .
To do this, we have to short circuit the ammeter input device and turn slowly R2, until we can read 0-0-0 in the displays.

Use the resistor R1 to calibrate the current level. Later we will see how to regulate. The circuit is designed to integrate it into our power supply.
We now need to have a look at a typical configuration of a power supply.

Here is the outline sketch:

Between the terminals of R1 we will extract two wires and lead them to the ammeter intake.

Have a look.

The value of that resistor R1 will give us the full scale of the ammeter. With a resistance of 0.1 Ohm we get a scale of 0 to 10 Amperes. And with a 1 ohm resistor the scale range is 0 to 1 Amperes.
The resistor must be 5 Watts and 1% tolerance.

The wiring diagram.

Download

The circuit board.

Download

The scheme and the circuit board should be in the same folder and they should have the same name, you should only change the extension to .sch for the scheme and to .brd for the circuit board, this way both of them will be recognized and associated by Eagle.

To calibrate the ammeter, put a load on the terminals of the power supply and measure their current with a tester. Turn R1 until you read in the displays the current we're measuring with the tester.

A picture of our ammeter in one of our power supplies.

This power supply has a digital voltmeter (red) and a digital ammeter (green).

If you don´t know how to make printed circuit boards, click here