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3 digits Digital Ammeter

Here is a digital Ammeter based on PIC16F684 and ACS712 current sensor. The measured DC orAC current will display on 3 digits 7-segment with resolution 100 mA. The current sensor in thisproject is ACS712ELCTR-30A-T from Allegro(I got from ebay). It can measure the AC or DCcurrent up to 30A with 66 mV/A output sensitivity. This project identical to my volt meter project

except the microcontroller not same.

SchematicThe microcontroller PIC16F684 reading analog value from the ACS712 current sensor output andconvert to curent for diplaying on 7-segment. All 7-segments are commond anode type anddriven by PNP transistors. Actually, this circuit suitable for measuring DC current e.g. solar panel

to battery, battery to load.

3 digits Digital volt meter http://coolcircuit.com/project/digital_amp_meter/picmicro_digital_amp_...

1 trong 3 9/26/2012 7:13 AM

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Calculating volt to amp for Vcc 5V

From ACS712 data sheet we know :

0 A = Vcc/2 = 2.5V or 512 analog counts or 0x200.Sensitivity 66mV/A for 30A version.

SoVolt at 30A = 2.5V + (66mV/A x 30A) = 4.48V or 917.504 analog countsVolt at -30A = 2.5v - (66mV/A x 30A) = 0.52V or 106.5 analog counts

--------------------------------------------------------------------Elenco 9440 Breadboard With JW-350 Jumper Wire SetExtech EX330 Mini Multimeter with Built In Thermometer

--------------------------------------------------------------------

With basic math linear equation

y = mx + b ----------- Equ. 1m = (y2 - y1) / (x2-x1) -------------Equ.2

So we get

m = (30-0) / (917 - 512) = 0.074

substitute m in Equ. 1 at output 0A, we will get b

0 = 0.074*512 + bb = -37.888

thus, the final equation use in software is :

A = 0.074*(analog_counts) - 37.888

3 digits Digital volt meter http://coolcircuit.com/project/digital_amp_meter/picmicro_digital_amp_...

2 trong 3 9/26/2012 7:13 AM

Example :if analog counts = 512 we get 0 Aif analog counts = 917 we get about +30Aif analog counts = 106 we get about -30A

Any questions about ACS712 please refer to ACS712 FAQ page

6.2, 25.2 ,29.9 simulate by input ADC value in firmware. 0.3 I use 3.3V and 10 ohm/10w

resistor.

The PCB track and wire of the input current in this project is used for measuring small current(forlearning). If you want to measure up to 30A the PCB track and wire of input current should be

large enough.

Schematic and firmware This is zipped file for picc source code,firmware and schematic for this project

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3 digits Digital volt meter http://coolcircuit.com/project/digital_amp_meter/picmicro_digital_amp_...

3 trong 3 9/26/2012 7:13 AM