电流表电压表+液晶面板电路,Voltmeter + Ammeter LCD panel 
Introduction
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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. Technical Specifications
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. Schematic
------------------------------------------------------------------------------ Bellow you can see the multimeter schematic. There are some components in the parts list marked as "Do Not Assemble". That components was needed in a previous software edition. Current software version doesn't need them, so you just don't add them. Maybe in a future version of the multimeter there will be a simpler PCB with simpler electronic diagram too. 
click /static/ic5/dianlu/image for higher resolution
PCB
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PCB files are >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.
After soldering all the parts on PCB:
make two cross connection on PCB (see "Layout - bottom side"). short L1 pads. place U2 element (+12V voltage regulator) on heatsink . pay attention on right polarity of D1 and D2 elements. Wider side of silk screen layout, where part number is placed, is CATHODE. Layout - bottom side 
Layout - top side
Parts List
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Element Value/Type Case Remarks
R1 100k 1206
R2 100k 1206
R3 10k Potentiometer
R4 30k 1206
R5 10k 1206
R6 10k 1206
R7 7k5 1206
R8 7k5 1206
R9 500R Potentiometer
R10 500R Potentiometer
R11 5k1 1206
C1 100n 1206
C2 100n 1206
C3 100n 1206
C4 100n 1206 Do Not Assemble
C5 100n 1206 Do Not Assemble
C6 100n 1206 Do Not Assemble
C7 100n 1206 Do Not Assemble
C8 100n 1206 Do Not Assemble
C9 100n 1206 Do Not Assemble
C10 22u/6V SMD A
C11 10n 1206 Optional element - protect Q1 against voltage peek after switch off fan. Most of the computer type fans which I tested didn't produce voltage peeks dangerous for Q1
C12 10u/50V
L1 47u 1210 Do Not Assemble - cross PCB pads
D1 DIODE SMD A Optional element - protect Q1 against voltage peek after switch off fan. Most of the computer type fans which I tested didn't produce voltage peeks dangerous for Q1
D2 DIODE SMD A e.g. SK310A
U1 7805 TO-252 Voltage regulator +5V, e.g. LM7805
U2 7812 TO220 Voltage regulator +12V, e.g. LM7812
U3 ATMEGA8 TQFP32
LCD GOLDPIN 1x16
J1 GOLDPIN 1x2 FAN_CON - fan connector
J2 GOLDPIN 1x1 +12V_CON - optional +12V supply connector
J3 GOLDPIN 1x1 +35V_CON - main supply connector
J4 GOLDPIN 1x3 ground and measured signals
S1 SWITCH
Q1 MOSFET N SOT-23 e.g. BSS-138 (fan current lees than 200mA) Programming
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Because ΅C is in TQFP package, we can program it after soldering all components on PCB. After that, programming is quite easy to perform. Programming signals are delivered through LCD connector. To make the programming cable, you can use an old PC HDD cable. Picture of my programming cable is shown here:
Remembered, that during programming, the circuit must be supplied with +5V. Depending on your programmer, supply voltage is provided either by programmer, or from separate power supply unit. Programming cable connection list
LCD Pin number LCD signal ΅C signal/Pin Prog signal
1 GND GND GND
2 VCC VCC VCC
4 RS SCK / PB.5 SCK
5 RW MISO / PB.4 MISO
6 EN MOSI / PB.3 MOSI
10 D3 RESET RESET
Download .hex file
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. Installation in PSU and Regulation Mount multimeter to PSU according to the diagram below: 
Connectors and regulation elements
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ELEMENT ACTION
S1 Setup button
When pushing this button the shunt resistor value appears. If the resistor value is known, repeat button pushing until correct value reached. If r
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