The initial schematics for the first PCB prototype is done.
It can be found in the git opendcm repository:
The changes from breadboard prototype are related mostly to increased over-voltage protection. The voltage supply of the input buffer LTC2057HV was increased to ± 30V, which will protect up to ± 40V with 1K resistor in series. Because the automatic voltage range switch ADG5419 is rated maximum to ± 22V, additional 1K resistor in series was added to the 20V range op-amp buffer LTC2057HV powered by ± 22V. By this way if input voltage is increased to ± 40V, the input voltage of the ADG5419 switch will be limited to ±22V by the power supply of the LTC2057HV buffer on the pin 8.
There are no changes in the ADC section at all:
The power supply and reference section:
The power supply will be more complicated as I though in the beginning. It should provide 7 positive and negative voltages. I'm not sure now if an AC with isolated transformer or step-up dc-dc converter from battery will be used as main power supply. The current consumption which I measured only on analog part, except the uController, was ~15mA, which is suitable for battery powered supply.
The next thing which I have to experiment is the connection between the ohm-meter and the voltmeter input.
The final multi-meter prototype will contain 3 PCB - one for the voltmeter and the ohm-meter, second for the current meter and the third for the power supply.
No comments:
Post a Comment