Inverting PS_ON levels



  • I recently upgraded to a Meanwell 24V PSU and it's finally time to wire up the remote on/off feature of the Duet/PSU. Sadly the PSU operates at inverted logic levels compared to the Duet PS_ON terminal.
    My idea was to take the PS_ON signal and hook it up to a RPi Zero W that I already have streaming a video. With the RPi I want to invert the signal and wire it to the PSU RC+. The RC- terminal would be wired to ground.

    Is this a valid way to do this?



  • Keep in mind that the GPIO pins are 3.3v, however, it does sound a little complex just for inverting a signal.

    I have a Meanwell supply with an optocoupler and a couple of resistors to invert PS_ON.
    If you're handy with a soldering iron it's another possible solution.



  • I've recently wired up one of those PSUs with an inline logic inverter, which I had from a radio control plane, connected to the PS_ON. I reckon your plan should work. The rpi will need to connect the RC+ on the PSU to ground/RC- to turn off the PSU. RC+ can float open circuit or be connected to the +5v standby to enable the PSU. The PSU labelling is confusing, but think of RC+ as the signal wire to switch, RC- as ground, and +5v as +5v. The only problem I can think of is that the standby 5v only supplies 500mA - that might not be enough to power the duet and rpi....



  • @insertnamehere said in Inverting PS_ON levels:

    I have a Meanwell supply with an optocoupler and a couple of resistors to invert PS_ON.
    If you're handy with a soldering iron it's another possible solution.

    Soldering is not an issue, how did you make a resistor based inverter?

    @pawprinter said in Inverting PS_ON levels:

    I've recently wired up one of those PSUs with an inline logic inverter, which I had from a radio control plane, connected to the PS_ON. I reckon your plan should work. The rpi will need to connect the RC+ on the PSU to ground/RC- to turn off the PSU. RC+ can float open circuit or be connected to the +5v standby to enable the PSU. The PSU labelling is confusing, but think of RC+ as the signal wire to switch, RC- as ground, and +5v as +5v. The only problem I can think of is that the standby 5v only supplies 500mA - that might not be enough to power the duet and rpi....

    I have a separate 5V PSU wired, so that will be a non issue.



  • @nxt-1 +5V is from the Meanwell aux supply.
    0_1549362828552_schemeit-project-2.png



  • @insertnamehere are the 5V @ 500mA (says 300mA in the datasheet) enough to power the Duet reliably?



  • @devleon In the OPs case possibly not. I'm using a Meanwell HFG600 which is 5V @ 500mA in the spec.
    I don't have a panelDue attached and fans all run off the 24V.
    I've seen no problems using a 500mA supply over 100s of hours printing.



  • @insertnamehere said in Inverting PS_ON levels:

    @nxt-1 +5V is from the Meanwell aux supply.
    0_1549362828552_schemeit-project-2.png

    I'm sorry to dig up this old thread, but I finally can to actually using this schematic. According to the datasheet, the 24V PSU needs: "RC+/RC- : 4 ~10V or open = power on ; 0 ~ 0.8V or short = power off" as a remote control signal. I soldered the little circuit together, but when I connect +5V and GND to the two terminals of my 5V PSU and measure the RC+ output of this diagram, I measure just 3.3V to GND. Also did you leave RC- floating or tied to GND in your printer?

    While thinkering with the optocouper, I came to think if there is any good reason to not connect the transistor straight across the RC+ and RC- terminals? As I see it, this would create a short or open based on PS_ON controlling the PSU just as well as a voltage applied. If I am mistaken, please correct me 🙂



  • @nxt-1 said in Inverting PS_ON levels:

    While thinkering with the optocouper, I came to think if there is any good reason to not connect the transistor straight across the RC+ and RC- terminals? As I see it, this would create a short or open based on PS_ON controlling the PSU just as well as a voltage applied. If I am mistaken, please correct me

    Yes, I think this is the way to go.



  • Could someone check if RC- is the same as GND of the output?



  • @fma said in Inverting PS_ON levels:

    Could someone check if RC- is the same as GND of the output?

    I measure 193mV between RC- and V- of my HPRG200-24.



  • I had the same problem and solved it with a simple 7400 NAND gate chip: https://forum.duet3d.com/topic/412/inverting-ps_on



  • So, you wired RC- to GROUND?



  • @tomasf said in Inverting PS_ON levels:

    I had the same problem and solved it with a simple 7400 NAND gate chip: https://forum.duet3d.com/topic/412/inverting-ps_on

    Mind sketching up a quick diagram?



  • @fma said in Inverting PS_ON levels:

    @nxt-1 said in Inverting PS_ON levels:

    While thinkering with the optocouper, I came to think if there is any good reason to not connect the transistor straight across the RC+ and RC- terminals? As I see it, this would create a short or open based on PS_ON controlling the PSU just as well as a voltage applied. If I am mistaken, please correct me

    Yes, I think this is the way to go.

    I tried it, but I forgot the signal needed to be inverted. As a result, this way it is functional but reversed. I not proficient enough with electronics to know if there is anything I can do to fix this, with the stuff I got laying around.
    0_1558556038259_2019-05-22 22.12.40.jpg



  • This post is deleted!


  • @nxt-1

    Sorry, I've not been online to answer earlier.

    I leave RC- open and just connect to the RC+ input.
    Are you using the 5V aux from the Meanwell or a separate 5V supply?



  • @fma said in Inverting PS_ON levels:

    @nxt-1 said in Inverting PS_ON levels:

    While thinkering with the optocouper, I came to think if there is any good reason to not connect the transistor straight across the RC+ and RC- terminals? As I see it, this would create a short or open based on PS_ON controlling the PSU just as well as a voltage applied. If I am mistaken, please correct me

    Yes, I think this is the way to go.

    Hmmm.... let me check.

    TO TURN ON SUPPLY.
    Duet PS_ON goes to ground to turn on power. PS_ON ground will turn on the opto diode.
    Opto diode on will cause the transistor to go ~ short. Short on Meanwell RC+ to RC- will turn OFF the Meanwell supply.

    If you connect emitter/collector of the opto across the RC+ and RC- of the supply this will not invert the PS_ON signal. That is why the emitter resistor is needed.



  • @nxt-1 said in Inverting PS_ON levels:

    @fma said in Inverting PS_ON levels:

    @nxt-1 said in Inverting PS_ON levels:

    While thinkering with the optocouper, I came to think if there is any good reason to not connect the transistor straight across the RC+ and RC- terminals? As I see it, this would create a short or open based on PS_ON controlling the PSU just as well as a voltage applied. If I am mistaken, please correct me

    Yes, I think this is the way to go.

    I tried it, but I forgot the signal needed to be inverted. As a result, this way it is functional but reversed. I not proficient enough with electronics to know if there is anything I can do to fix this, with the stuff I got laying around.
    0_1558556038259_2019-05-22 22.12.40.jpg

    This will not invert the PS_ON signal. The PS_ON signal from the Duet is a "Ground = On" and the Meanwell is "Open = On". The Emitter resistor inverts the signal.



  • Yes, you're right. You need to use @jv43 config, using 5V from Meanwell. So this only works for this power supply. If the 5V is from another source, and this source turns off, the Meanwell remains ON 😞


 

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