hi,
Set VR1 for 0.5V and adjust VR2 to give 1.5V out [Y]
That CA3140 seems to be limiting at a lower voltage than I would expect, I'll check it out.
Once you have set the VR1 pot to 0.5V and VR2 to give 1.5V out you can connect this to your PIC adc input and try your PIC program.
Adjust VR1 as you test with different voltages, but leave VR2 unchanged..OK
When you are happy with that test, connect the AD736 to the CA3140 as shown in the dwg,,, remove the test pot input first.
Will be moving over to veroboard soon.
I am currenlty doing the drawing for the veroboard. But it will take me a while.
Here is my Vero drawings.
Can you give it the once over?
I also have a small question:
The AD736 is producing say 0.4 mv when there is a 40 Watts load on the live wire, and when there is close to 2000 watts it goes up to 1.3mv.
Looking at those figures I would expect them to be proportional but they do not appear to be.
When connected to the CA3140 the change is almost negligible.
Also the moving up from 0.4 to 1.3 is almost a digit per second and the same for going down, appears to be a capacitor problem!!??
Thanks.
hi,
I'll look at the vero layout.
According to the datasheet the current clamp on its most sensitive range is 1mV/0.1A, so thats 10mV/Amp, so for a 2KW [8 amps] you should get 10mV * 8 about 80mV. [ you did say sometime ago this what you did read OK]
This 80mV being amplified by 3 using the CA3140 should give a adc input voltage of 240mV, which for a 10bit adc with a 3Vref gives an adc conversion value of 81 decimal.
By scaling the output from the AD736 using the CA3140 the adc conversion value is directly proportional to current.!
In this case: 81 counts = 8.0Amps.
Yes the clamp itself when connected to my DMM I can see 0.008 volts AC for about 40 watts load and when I add a 2000 watts load it jumps up to 0.084 VAC which is just about matches the figures you have.
hi,
Layout looks OK, always leave the pcb corners clear for pcb mounting pillars.
I think your comps list R5 is wrong.
Yes I realised and corrected it accordingly, seems you picked the earlier version
This look OK.
Be sure to meter in the correct points when measuring the AD763.
There is one thing I should mention:
The PIC has a battery and can provide +5 vdc, so I am using that to power the CA3140, will this has any effect? it is just that when I connect the +5v and the Vout and the GND to the PIC I get a reading of 2-3 decimal and when I removed the GND it jumps up to 1023 (max) and thats because the ADC is now receiving +5vdc.
I am somehow confused as to why the ouput of the AD736 is between 0.4mvdc and 1.3 mvdc.
Edit:
When nothing is connected to the PIC the ADC reading is at 51 decimal.
Never disconnect the 0V gnd from the PIC while applying +5V to Vss, especially when the other pins of the PIC maybe connected to other voltage sources,
The 2~3 mV is most likely noise pickup, you can trim this out with 10K thats normally on pins 1/5 of the CA3140 or do it in the program.
If the adc input pin is floating you will get pickup, low mV's.
It will be OK to power the CA3140 from the PIC's +5V.
I thought you said earlier that the PIC was powered by 3V.???
According to the datasheet the current clamp on its most sensitive range is 1mV/0.1A, so thats 10mV/Amp, so for a 2KW [8 amps] you should get 10mV * 8 about 80mV. [ you did say sometime ago this what you did read OK]
This 80mV being amplified by 3 using the CA3140 should give a adc input voltage of 240mV, which for a 10bit adc with a 3Vref gives an adc conversion value of 81 decimal.
By scaling the output from the AD736 using the CA3140 the adc conversion value is directly proportional to current.!
In this case: 81 counts = 8.0Amps.
hi,
We seem to be going around in circles.
Post a circuit diagram of how you have the AD736 and CA3140 connected showing ALL the power supply lines.
hi,
Questions ref the HR pic.
Q1:
Are V1 and V2 board sockets connected or isolated from each other.?
IF they are isolated, then how does pin4 of the 736 get its 0v connection.?
Q2:
Fig28 of the data for the 736 shows pin1 has be connected to pin8 via a 10uF capacitor.
Its hard to be sure looking at the pic, but the cap maybe in pin1.?
BUT its going the clamp [red wire] output.
You are showing the other output from the clamp [blue wire] going to pin 2,
its supposed to goto the Vs/2 [junction of the two 100k's]
Q3:
Why are the resistors marked '????' in the circuit.?
If its because you dont have a 4K7, then the pin3 resistor value is not critical, just use one of those 3 resistors.
Q4: Looking at Fig28 of the 736 data, pin2 requires a 1M0 connected to pin8 [Vs/2]
also Vin [clamp red wire] to pin2 is via a 100nF cap.
I did ask for a circuit diagram not a picture, I have had to reverse 'engineer' the pic into a circuit.
Look at my marked up image, the lines are just my tracing guides.
BTW: I thought you had decided to use fig28 of the 736 datasheet for the circuit.
Thanks. for the formula.The calculation for the 10 bit conversion is fairly simple.
Adc Value = [Vsig/Vref]/1023
You cannot power the CA3140 from the 9Vbty thats powering the AD736
because you have a virtual 0V Gnd at the junction of the two 100K's
Its a split battery.
Hi,
The proposed layout is the way that I would do it.
Lets know how it goes.
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