Voltage, Ampere Digital meter

  
This multimeter was designed to measure output voltage and current in a PSU, where the current sense shunt resistor is connected in series with load at the negative voltage rail. It needs only one supply voltage that can be acquired from main PSU. An additional function of the multimeter is that it can control (switch on and off) an electric fan used to cool the main heatsink. The power threshold at which the fan switches on can be adjusted using One Touch Button Setup. single uC ATMEL ATmega8 used to handle all the multimeter functions. voltage range 0-30V. voltage measure resolution 10mV. current measure resolution 10mA (depended on current sense resistor value). single, non isolated voltage supply. one side PCB. compact construction allowed to use the multimeter as panel meter. compatibility with standard LCDs based on HD44780 controller.
Voltage, Ampere Digital meter - schematic

After connecting ?C to prog, you should check, if ?C is "visible" for prog. When everything is fine, you can upload code to ?C. The code is available >here< .It is assumed that ?C is new and works with its internal RC clock at 1MHz. If not, set appropriate fuse bits to achieve above mentioned conditions. In addition Brown-out detector should be turned on by enabling BODEN fuse. Recommended Brown-out Reset Threshold Voltage is 4V. The next thing to do is to cross LCD soldering pads number 1 and 5. That's necessary to provide ground for LCD RW signal. After all, connect LCD module with the multimeter PCB. It is recommended to use a detachable connector for further expandability e.g. software upgrading. CAUTION This circuit itself doesn't work off the mains and there are not 220 VAC present, but PSU does. Voltages above 50 V are DANGEROUS and could even be LETHAL. In order to avoid accidents that could be fatal to you or members of your family please observe the following rules: DO NOT work if you are tired or in a hurry, double check every thing before connecting your circuit to the mains and be ready to disconnect it if something looks wrong. DO NOT touch any part of the circuit when it is under power. DO NOT leave mains leads exposed. All mains leads should be well insulated. DO NOT change the fuses with others of higher rating or replace them with wire or aluminium foil. DO NOT work with wet hands....



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