Perfect, thanks for clarifying.
As someone else noted the MCP3204 looks to be the chip you're referring to.
And the code is here: https://github.com/dc42/RepRapFirmware/blob/6b835cb3c8e9aa10113ae750151d9f9065116cd4/src/Heating/Sensors/CurrentLoopTemperatureSensor.cpp#L23
I'll report any more findings as I implement.
@fcwilt said in 48v on V_Bed by replacing SMD components?:
@mkelly said in 48v on V_Bed by replacing SMD components?:
I have been using an SSR but it limits the operating frequency and feels unneeded. The SSR being used right now is this one from automation direct
The point of not using an SSR would be to achieve a higher frequency than 50-60Hz, which is what the data sheet lists as the operating frequency for them.
This would also be a way to save costs by not requiring a separate circuit to drive a 48v device, either by an SSR or the mosfet selection I'm proposing.
I do not understand your concerns.
For a bed heater the frequency range you listed is fine. Bed heaters rated for line voltage (110/220 VAC) are usually more powerful which is a good thing.
Since the SSR connects directly to the bed heater output on the Duet it is about as simple as it can be.
What do think you would improve by doing what you propose?
Thanks.
Frederick
Hi Fred. I never said I wanted to be driving a bed heater from the V_bed line, but rather I wanted to drive 48v at a higher frequency (ideally 1-2khz range). This is an exploration at the possibility.
I have been using an SSR but it limits the operating frequency and feels unneeded. The SSR being used right now is this one from automation direct
The point of not using an SSR would be to achieve a higher frequency than 50-60Hz, which is what the data sheet lists as the operating frequency for them.
This would also be a way to save costs by not requiring a separate circuit to drive a 48v device, either by an SSR or the mosfet selection I'm proposing.
I am exploring the possibility of driving 48V on the V_bed rail on a Duet 2 Ethernet. From what I see in the schematics the components that would need replacing are TR2, D5/6, and C91
For TR2 a 60V mosfet could be used instead, such as a IPD031N06L3 G
For D5 I'm struggling to determine what the allowable forward voltage is. The worst case I found was 30V for SOD-523F package, ie RB520S30. But it could also be 75V if it was a 1N4448WT
Looking at a close up of the SMD it appears to have an E2 marking, which makes me think it's a 75V version
I'm also thinking the LED is going to be affected, meaning replacing R65 with an 10k resistor.
For C91 I'm thinking this is easy enough to just replace with another 10uf capacitor (what appears to be a 1206 package) with a higher voltage such as this: CL31A106KBHNNNE
Does this all make sense? Am I missing something obvious?
Granted this is all easy to do on paper, and not something very easily done on an existing board. The first step is just figuring out the circuit, then worrying about how to actually do it.
You were correct, x1 changed to x10 now I'm measuring 5.3V.
For the arduino output has a positive width of 1.78ms(~560Hz)(@ the full 5.3v) with a repetition frequency of 50Hz. Total Pulse width is 20ms
Here's the test code, intended to cycle the servo with a 2s pause:
#include <Servo.h>
Servo myservo; // create servo object
int pos = 0; // variable to store the servo position
void setup() {
myservo.attach(8); // attaches the servo on pin 8 to the servo object
}void loop() {
delay(2000);
// 120ms to travel 60 degrees
for (pos = 60; pos <= 120; pos += 5) { // travel 60 degrees
myservo.write(pos); // tell servo to go to position in variable 'pos'
delay(10); // waits 10ms for the servo to reach the position
}
Apologies, sorted out the issues with the measurement, now I'm getting a clean signal from the PWM. Here's a picture from the scope with only 500mV being measured on the square wave at 50Hz. I have isolated the wiring to such a degree that there is no chance of faulty wiring, if it was such a simple troubleshoot this wouldn't have taken so many steps to unravel.
This measurement is identical to the arduino controlled version. Which further increases the confusion why driving the servo off the Duet would have any impact on driving a digital servo.
Again here's the chart showing the operability of the servo using the exact same wiring:
I also found a servo catalog chart with something interesting. It specifies the Control circuit for the HS-645MG as "ANALOG" but the HS-7954SH specifies a "G2 DIGITAL" Control circuit. It is not clear if this is referring to the internal control circuit (likely) or something relating to the PWM (unlikely), but perhaps that means something to you.
The other options for the other digital servos in the chart are "G1 Digital", "G2.5 Digital", "HR Digital", "32bit Digital" and "EBL Digital"
At this point all I'd like to know is if anyone has successfully driven a digital servo off of the Duet? I'm thinking it's necessary to use an external circuit to drive the servo since it's taking so much effort to get the Duet to do it.
There's too much noise on the scope to get a good reading, but I was just reporting the measurements from the control signal.
Again, the digital servo works fine on an Arduino, which also drives the Analog servo of similar form factor.
The wiring on the duet can drive the analog servo just fine, meaning there's no issues with the wiring from a conductivity standpoint.
The only variable I can't control right now is how the Duet is outputting the PWM signal to drive a digital servo, and I'm not able to confirm if anyone has been successful in driving a digital servo off of a duet.
The arduino is only supplying a measured peak-to-peak 500mV on the control wire when driving the digital servo, the duet is outputting a measured peak-to-peak 1.5V. Both the old analog servo and new digital one operate at 6V on the power, so that's where we're currently set to switch between either option, at least until we get the digital working.
What frequency is the PWM operated at?
Good call, Just tried doing 20 degrees to see, no difference. Looking at the servo datasheet I'm seeing
Operating Travel: 40±5°/ONE SIDE PULSE TRAVELING 400usec
Direction: CLOCK WISE/PULSE TRAVELING 1500 TO 1900 usec
To try and eliminate variables I've also been using an Arduino driving a servo from 0-60°, it did seem to be driving the servo 60 degrees. I recreated the wiring diagram using an external variable power supply and confirmed I am able to drive the digital servo successfully using the voltage regulator and a relay. I confirmed this was true with analogs as well.
Meaning I only had the PWM pin connected to the arduino, and the voltage being driven elsewhere. Grounds were tied together for reference on a breadboard.
Again, with an arduino the digital servo and analogs commanded the correct move position every time
However, when I took this identical wiring arrangement, and only changing the PWM pin going into the PWM on the Duex, I am ONLY able to drive analog servos. The digital one continues to not move.
The only thing I can think of is the PWM frequency between the two devices is different. I'll probably hook it up to an osciloscope to see if I can see the frequency, but at this point I'm pretty compelled of the origin of the issue, and would be willing to go so far as to ship you a digital servo if necessary.
Forgot to upload the config first time. I'm shutting off all the heaters on the Duex just to be safe:
0_1548440073786_config.g
Tested two different analog servos, a little 9g one and the HS-645MG listed in the OP. Both worked without issue.
Still can't get the digital one to trigger.
Thanks. Right now we're just running the relay plugged into an always on so we don't have to have another variable
