DIY Stack and Stitch System

As mentioned earlier I developed a motor current sensor/probe based upon the Hall Effect, and built a breadboard to verify the operation. Then developed a PCB with a few added features and improved precision and removed offset bias due to single supply bias.

The PCBs finally arrived and I was able to assemble a board. Got all the parts soldered in for the +-2.5A version (still waiting on one part for the +-5A version) and did a preliminary check to make sure everything was in order and powered up.

I've included the ability to power the sensitive analog circuitry 4 op amps from the filtered motor supply or the regulated +5V, and the DC to DC converter negative analog supply voltage from the same (just in case). +5 volts is required for the Hall Effect sensor. The entire design is based upon precision differential techniques which don't depend on precision components, nor supply or regulator voltages to a 1st order. Techniques learned over my career with precision electronics, applied to keep from using expensive precision components.

Checked the 5 volt regulator output and installed the jumpers to power from this initially. Set the negative DC to DC converter voltage, and then the offset potentiometers to 0.000 volts for the Sine and Cosine outputs. Switched the jumpers to the motor supply (~12V), the offsets remained at 0.000 volts, then changed the negative supply from -5 to -10 volts, the offset remained at 0.000 volts. This is what should happen based on the design concepts, almost complete independence for supply voltages.

Then hooked up a stepper motor and 1% sense resistors and went through a brief calibration. Hooked up a O-Scope and the waveforms looked really nice, quick response but not much chopper noise thanks to the dual 3rd order active filters.

Now came time to evaluate the current measurement precision. Used a Fluke 87 and 77 to measure current and voltages, along with some 1, 0.47 and 0.22 ohm 1% resistors. Used my very old lab supply to supply the current, and did a calibration at 1000ma for both Sine and Cosine for 1.000 Volt/Amp. Then ran the current from 0 to 1.7amps (range of my motors) to check the linearity and precision, judge for yourself.

Current Input ma, Current Reading Output mv:

0, 0.0
12.12, 12.3
30.13, 30.3
50.6, 50.9
76.0, 76.2
100.8, 101.0
125.8, 125.8
168.9, 168.9
200.3, 200.2
256.5, 256.3
301.0, 300.7
350.3, 350.0
401.3, 401.0
451.0, 451.0
500.0, 500.0
600.0, 600.0
700.0, 700.0
800.0, 800.0
900.0, 900.0
1000, 1000
1100, 1100
1501, 1500
1700, 1698

From 100ma to 1700m the error is less than 0.2%.

Hall Effect Stepper Motor Current Probe

Blank PCB

Assembled PCB, Note Negative Supply DC to DC Converter URC, 4 Potentimeters for Offset and Scale Sine and Cosine Trim RC, Power Connector ULC, Motor Input and Output LC, and Analog Output Connectors (2) RC & BR.

Another view

NEMA 17 Stepper Motor Current Waveforms for Start and Stop, note profiles from Trinamic Controller

Stepper Motor Currents, Scale is 500ma/Div

Best,