Microcontroller Voltmeter / Ammeter with LCD

Rectifier bridge voltage. See U2 element you used data sheet to know about maximum voltage it can work properly. On the other hand the minimum voltage on that pin mustn`t drop bellow c. a. 9V, or 6. 5V if low drop type U2 and U3 voltage regulators were used. Multimeter is suitable for voltage and current measurement in PSU, where current sense shunt
Microcontroller Voltmeter / Ammeter with LCD - schematic

resistor is connected in series with load and is in negative rail. Because µC is in TQFP package, we can program it after soldering all the elements on PCB. It makes programming quite easy to perform. Programming signals are delivered through LCD connector. To make the programming cable, you can use old PC HDD cable. Picture of my programming cable is shown below. Remember, that during programming multimetr circuit must be supplied with +5V. Depending on your programmer, supply voltage is provided either by programmer, or from separate power supply unit. After connecting µC to prog, you should check, if µC is "visible" for prog. When everything is fine, you can upload code to µC. The code is available here. It is assumed here, that µC is new and works with its internal RC clock at 1MHz. If not, set appropriate fusebits to archive 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. It is necessary to provide ground for LCD RW signal. After all, connect LCD module with the multi meter PCB. It is recommended to use a detachable connector for further expandability e. g. software upgrading. Picture of PCB is here. There are two version of PCB - normal and mirrored. I think, that anyone who makes PCBs will know, which one should be used to produce right PCB. *...

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