Current Meter

[mikefox]

Hi guys,

I need to ask for a little help, I'm building a current meter for a client, and I'm having difficulty working something out.
I am using a 16F877A with ADC channels 0 to 2 used to measure voltage and current, this all works fine, what I'm having trouble with is calculating current drawn over a period of hours, measured in amp-hour. The idea for this is to show the total current in or out of the system in a day.

Please, if anyone can help, I could use any tips you might have.

Mike

[dmairspotter]

a long time ago in a PC. I basically took an amp reading every second and added 1/3600th of the reading to a register. Basically integrating the amps to get amp hours. Seems like you could do something similar, with different math order, in the PIC.

[mikefox]

Thanks mate, this code seems to do the job.

avg_curr1 = avg_curr1 + (curr0 / 10)
avg_curr0 = avg_curr1 / 3600

Mike

[Squibcakes]

This sounds like something I could use....

I wouldn't mind replacing the old analog current / volt meter in my 30amp load tester with a digital version, including aHr Capacity.

The current shunt we have produces 50mv max at full load (50amp)

How could this be measured using a pic.. (Use op amp???) of sort?

I would like to know if anyone else has done this before.

On an other topic, has anybody made their own wire wound resistors before?

Cheers

[Charles Linquis]

I have built several current meters using Allegro hall-effect sensors. They offer perfect isolation and have no voltage drop. Depending on the model, they have an output of 20-133 mv/Amp. When measuring DC current, I usually use a rail-to-rail op amp to shift the output to near zero volts (the quiescent output voltage of the sensor is VCC/2) and amplify the output a bit before feeding it into the A/D converter.

Fantastic devices, very accurate and stable. Much neater than using sense resistors.

[MikeTamu]

I have used the Maxim 4172 Current Sense chip and found it to be very easy to impliment and precise.

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1654

[pramodsinha]

Hi guys,

I need to ask for a little help, I'm building a current meter for a client, and I'm having difficulty working something out.
I am using a 16F877A with ADC channels 0 to 2 used to measure voltage and current, this all works fine, what I'm having trouble with is calculating current drawn over a period of hours, measured in amp-hour. The idea for this is to show the total current in or out of the system in a day.

Please, if anyone can help, I could use any tips you might have.

Mike

Why not to use 16f676 for the cost consideration as it cost in delhi is Rs.35 only

[Squibcakes]

Charles,

I finally received my free samples from Allegro today.. gees these guys are slow. I hope that they are worth the wait!

[RYTECH]

what resistor values should i use for the max4172 if my input source voltage is 5v's and my meter should give values for current between 0 and 2 amps.???