Thanks Dwight and Jiggy-Ninja for your patient and comprehensive instruction.
+1 to both of you.
Just to show you I was paying attention:
Waveform for Setpoint = 650 mA (previous oscillations caused by mosfet not making good connection)
Scope V/Div = 1V
Scope Time/Div = 2 uS
That looks like some terrible oscillation on the output there, but I can't tell without knowing the scale.
)
Got rid of oscillations and replaced photo of one without oscillations. (caused by mosfet pins not conducting enough current due to poor connection in breadboard.)
int pwm_pin = 3;
int pwm_cmd = 64;
int voltage_cnts;
float voltage;
float current;
void setup()
{
// put your setup code here, to run once:
Serial.begin(115200);
pinMode(pwm_pin,OUTPUT);
}
void loop()
{
// put your main code here, to run repeatedly:
voltage_cnts = analogRead(A0);
voltage = voltage_cnts * 0.004887585532746823069403714565;
current = voltage/2;
Serial.println(current,7);
// delay(1);
if (current < 0.650 && pwm_cmd < 255)
{
pwm_cmd ++;
analogWrite(pwm_pin, pwm_cmd);
}
if (current > 0.650 && pwm_cmd < 255)
{
pwm_cmd --;
analogWrite(pwm_pin, pwm_cmd);
}
}
Electronic SOURCE is RC 3S 2200 mAh LIPO BATTERY (45C, capable of delivering 99 A for 1.3 minutes so if Constant Current Electronic Load is not regulating , it can get real ugly, real fast !)
Terminal Capture of Current measurement calculated as Vcurrent sense/2 ohms
2.3655912
2.3460409
2.2653958
2.4217987
2.2287390
2.3460409
2.2165200
2.2360703
2.3167154
2.3924732
2.1505377
2.4193549
2.2702834
2.1480939
2.4217987
2.2678396
2.3435971
2.2067449
2.2165200
2.3142716
2.2067449
2.4022483
Files Included
Photo of circuit
Photo of waveform obtained with "Old School" scope set to Differential Mode (Select = ADD, Ch-2=INV)
Terminal Capture of Current measured (Vcurrent sense resistor/2)
Terminal Capture of Current measured with setpoint = 0.650 A (650 mA = 1.3 V)
Photo of DMM with 650 mA setpoint (voltage = 0.65 * 2)
Just to prove that it was regulating current, I changed the setpoint to 0.650 A
0.6500489
0.6353861
0.6256110
0.6085044
0.6451613
0.6451613
0.6085044
0.6085044
0.6427175
0.6451613
0.6256110
0.6133920
0.6353861
0.6500489
0 0.6256110
0.6231672
0.6231672
0.6451613
0.6256110
0.6256110
0.6231672
0.6353861
0.6256110
0.6085044
0.6329423
0.6549365
0.6256110
0.6451613
0.6451613
0.6085044
0.6256110
0.6231672
0.6549365
0.6133920
0.6133920
0.6451613
0.6353861
0.6133920
0.6500489
0.6549365
0.6256110
0.6280548
0.6549365
0.6500489
0.6329423
0.6500489
0.6304986
0.6280548
0.6549365
0.6451613
0.6329423
0.6647117
0.6353861
0.6598241
0.6695992
0.6280548
0.6280548
0.6647117
0.6647117
0.6329423
0.6622679
0.664711
Voltage on sense resistor is 1.310 V for setpoint = 650 mA (V = I*R= 0.650 A * 2 ohms =1.300 V
(right click on photo of meter and select "Open image in new tab"
FYI, you can see the op amp power supply voltage (8.5vDC) on the LCD of the P.S. underneath the DMM. To view it, right mouse click on photo and select "Open Image in new Tab".
BTW, that DMM was purchased in 1995. (21 years ago. still working good...)
ClearTerminal_Capture_Constant Current Electronic Load_10.02.2016_18.23.00.txt (18.7 KB)