CAN connected heated bed? Sammy?
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Hi All,
I'm back looking at solutions for a rotating heated bed for my polar printer. This time I'm thinking of passing 240v and CAN in via a slip ring.I was thinking a Sammy-C21 might be a good budget solution, or perhaps a tool board?
Is there firmware support on a Sammy for a temperature sensors and heater control? Plan is to use an SSR to run the 240v bed and a local DC supply to power the Sammy / tool board.
Any thoughts would be much appreciated.
All the best.
Barry M -
@cncmodeller the standard SammyC21 code doesn't have dedicated thermistor inputs that support automatic thermistor input calibration, whereas the tool board does. OTOH the tool board is designed for 12-24V input, whereas the SammyC21 just needs a 5V supply. It may be that you could power the tool board from 5V fed into the IO connector, but this is something we haven't tried.
You can use a thermistor with ordinary analog inputs on the SammyC21. The accuracy will be reduced, however as the temperature range for a bed heater is smaller than for a hot end, you can mitigate this by choosing an appropriate ratio of thermistor series resistor to thermistor resistance.
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@dc42 said in CAN connected heated bed? Sammy?:
You can use a thermistor with ordinary analog inputs on the SammyC21. The accuracy will be reduced, however as the temperature range for a bed heater is smaller than for a hot end, you can mitigate this by choosing an appropriate ratio of thermistor series resistor to thermistor resistance.
Thanks @dc42 , I have a SammyC21 but I've not touched it yet, so I can prototype what you suggested.
I take it form what you've said I can 'simply' identify the SammyC21 as the relevant IO for a temp sensor and bed pwm? If I get a Thermistor with a small temperature range, and then offset the reading with a series resistor?
Sorry for the follow up. Thermistors aren't something I have looked at before.
All the best,
Barry M -
@cncmodeller yes you can configure the SammyC21 to be the bed heater and bed temperature sensor.
For the series resistor, if you use a standard 100K bed thermistor then I suggest you use a thermistor series resistor of about 33K. That will give best accuracy over a range of about 15C to 100C.
To save passing 240V through slip rings, it may be possible to heat the bed by induction. There are some inexpensive single-ring domestic induction hobs available, for example https://www.amazon.co.uk/CIARRA-Induction-control-Polished-Crystal/dp/B08B664MBC. It might be possibly to hack one of those to heat the bed. You would still need to get a temperature reading from the bed, but that might be as simple as connecting a PT1000 sensor via slip rings.
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@dc42 Thanks for the info, will give it a go over the next week or so.
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Hi All,
After quite an interlude I've got all the parts for my heated bed and am in the process of testing my setup.For general information here's a picture and a couple of things that I've noticed worth passing on / discussion.
The pwm on the SammyC21 pin pa12 isn't zero when the board is initialised. It drops to 0% as soon as the board is connected to can and configured. I was thinking of adding a relay to isolate the 240v until setup is complete. Is this something we tend to worry about or should I just accept short transients during startup?
The temperature is a little noisy as @dc42 suggested, it wanders +- 1 or 2 deg . Is there anything I can do to clean it up? Perhaps a capacitor from singal to ground? I'm using pa08 for the thermistor and a 33k series resistor as @dc42 suggested.
The SammyC21 takes several seconds to initialise so a longer dwel during start-up is required to allow it to start before sending commands.
I've also got this error when auto tuning, the tune is complete, I'm guessing its because of the noisy temperature signal:
Warning: heater behaviour was not consistent during tuning Auto tuning heater 0 completed after 3 idle and 25 tuning cycles in 1207 seconds. This heater needs the following M307 command: M307 H0 R2.979 K10.675:0.000 D3.48 E1.35 S1.00 B0
these are my sensor and heater setup commands from config.g
M308 S0 P"124.pa08" Y"thermistor" R33000 T100000 B4138 M950 H0 C"124.pa12" T0
The slip ring is fitted, just about to start final assembly.
Anyway at least som progress now...
Any constructive thoughts would be great!
All the best
Barry M -
@CNCModeller said in CAN connected heated bed? Sammy?:
The pwm on the SammyC21 pin pa12 isn't zero when the board is initialised.
Try adding a 10K or 4K7 pulldown resistor between the pin and ground.
@CNCModeller said in CAN connected heated bed? Sammy?:
The temperature is a little noisy as @dc42 suggested, it wanders +- 1 or 2 deg . Is there anything I can do to clean it up? Perhaps a capacitor from signal to ground?
Yes, that may help.
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@dc42 said in CAN connected heated bed? Sammy?:
@CNCModeller said in CAN connected heated bed? Sammy?:
The pwm on the SammyC21 pin pa12 isn't zero when the board is initialised.
Try adding a 10K or 4K7 pulldown resistor between the pin and ground.
@CNCModeller said in CAN connected heated bed? Sammy?:
The temperature is a little noisy as @dc42 suggested, it wanders +- 1 or 2 deg . Is there anything I can do to clean it up? Perhaps a capacitor from signal to ground?
Yes, that may help.
Thanks @dc42, the capacitor has helped it now wanders consistently with the nozzle reading so I'm ok with that, will try another bed heater autotune tomorrow.
Unfortunately my 5k6 pulldown resistor doesn't seem to make much difference.
I'll ponder some more tomorrow, time for tea!
Many thanks again,
Barry M -
@CNCModeller said in CAN connected heated bed? Sammy?:
The temperature is a little noisy as @dc42 suggested, it wanders +- 1 or 2 deg .
Does it happen with the bed rotating? Slip rings tend to produce noise too, so in many occasions a single signal is transmitted by two or more slip rings in parallel. That way the noise is cancelled out.
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@o_lampe said in CAN connected heated bed? Sammy?:
@CNCModeller said in CAN connected heated bed? Sammy?:
The temperature is a little noisy as @dc42 suggested, it wanders +- 1 or 2 deg .
Does it happen with the bed rotating? Slip rings tend to produce noise too, so in many occasions a single signal is transmitted by two or more slip rings in parallel. That way the noise is cancelled out.
Hi @o_lampe, the slip ring sends CAN and 240v to the SammyC21 and heater so this shouldn't be an issue. I'm just testing at the moment however and the slip ring isn't being used yet.
Many thanks for the tip though.
Cheers
Barry M