Inverting PS_ON levels

Nxt-1 · 4 Feb 2019, 15:54

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?

insertnamehere · 4 Feb 2019, 23:03

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.

pawPrinter · 4 Feb 2019, 23:05

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....

Nxt-1 · 5 Feb 2019, 09:21

@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.

insertnamehere · 5 Feb 2019, 10:44

@nxt-1 +5V is from the Meanwell aux supply.

devleon · 2 May 2019, 13:03

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

insertnamehere · 2 May 2019, 22:15

@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.

Nxt-1 · 21 May 2019, 21:56

@insertnamehere said in Inverting PS_ON levels:

@nxt-1 +5V is from the Meanwell aux supply.

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

fma · 22 May 2019, 06:23

@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.

fma · 22 May 2019, 09:06

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

Nxt-1 · 22 May 2019, 09:29

@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.

tomasf · 22 May 2019, 09:57

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

fma · 22 May 2019, 10:49

So, you wired RC- to GROUND?

Nxt-1 · 22 May 2019, 11:32

@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?

Nxt-1 · 22 May 2019, 20:16

@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.

fma · 23 May 2019, 06:08

This post is deleted!

insertnamehere · 24 May 2019, 01:07

@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?

insertnamehere · 24 May 2019, 01:14

@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.

insertnamehere · 24 May 2019, 01:17

@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.

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.

fma · 24 May 2019, 05:20

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