Not getting correct output signal from SparkFun Current Sensor Breakout - ACS723, PN SEN-13679

[PSS]

I am trying to figure out what I have done wrong wiring up the SparkFun Current Sensor Breakout - ACS723 (PN SEN-13679).

I have VCC connected to the 5 volt output from my adjustable power supply (set at 5 volts).

I have GND connected to the ground terminal on the power supply.

I have VOUT connected to my scope (and I tried my DVOM too just in case)

On the other side I have IP+ going to the solenoid I am operating and IP+ going to the device driving the solenoid (powering the solenoid). I tried reversing those with no change.

When I hook up the scope I do not get the correct current trace for the solenoid operating. This is the scope trace I get from the VOUT pin:

I checked the current with a clamp on current clamp and when I connect that I get the correct trace. This is what the current trace should look like (from scope connected to current clamp):

Looking for ideas on what I have done wrong to cause this.

Here is one of the tutorial wiring diagrams (note that this is for the low current version with gain circuitry).

https://cdn.sparkfun.com/assets/learn_t … ircuit.JPG

Also note that the pins on the wiring diagram don’t match the production parts - the GND and VCC positions appear to be swapped and 5v is labeled VCC. The parts I received do match the actual product pictures on the web site though. Maybe that is related to my problem?

Thanks,

PSS

[TS-Chris]

Hi PSS.

the pins on the wiring diagram don’t match the production parts - the GND and VCC positions appear to be swapped and 5v is labeled VCC. The parts I received do match the actual product pictures on the web site though. Maybe that is related to my problem?

It looks like when we revised the boards to use the newer IC, we swapped the VCC (5V) and GND pins on the edge of the board, then when we rewrote the tutorial we took new photos, but didn’t update the diagrams. VCC is 5V and GND is GND. If you had hooked that up backwards, that could have damaged the chip. I’ve let our tutorials team know about the diagrams and those should be fixed soon.

However, even if the chip were damaged, your scope is showing a rather large (32 volts peak to peak) AC voltage on the OUT pin, and if you have VCC and ground connected to a 5 volt DC power source, that isn’t possible. (The largest signal you should see is roughly 4 volts volt peak to peak if you’re measuring AC current.)

Are you absolutely sure you’re feeding the board 5 volts DC for power and not an AC voltage? What voltage is your solenoid being powered with and is it AC, DC or pulsed DC? Where are you connecting the ground lead from your scope? Did you purchase the sensor directly from SparkFun or through a distributor? If you purchased directly through SparkFun can you PM me your order or invoice number?

[PSS]

Thanks for the quick response.

I found the problem - bad ground on the scope leads (I was sure I checked that but after your reply I went back and checked everything again).

Here is the trace with the changed scope lead connection (yellow is the SEN-13679 board and blue is the clamp on hall effect output).

BTW - yes, I saw the swap and assumed the parts were labeled correctly so luckily I didn’t put the wrong voltage to the wrong pin.