How can I convert -24v NPN output to +5v?

[Azalin]

Hello,

I want to use an NPN proximity sensor as homing switch. I fed the sensor with an external 24v power supply so as the sensor is NPN the output is -24v. The BOB wants +5v on the limit switch input.

So I need to convert the -24v coming from the sensor to +5v. Is there a practical way to achieve this or should I give up and use a PNP sensor?

Thanks in advance.

Best,
Suat

Similar Threads:

• Output voltage from Output Board seems to be quite low?
• Can some please convert ...
• Just IN- CONVERT SINGLE 240/480V POWER TO THREE PHASE 415V OUTPUT
• Convert cc to hp ?

[john-100]

which BOB are you using ?

depending on the BOB you may be able to add a pullup resistor of about 200 to 300 ohms
between the BOB input and +5V

with the -24V power supply terminal connected to the BOB's common / ground
the sensors open collector NPN output will ground the BOB's input when triggered

when the sensor output is off
the pullup resistor will pull the BOB's input towards +5V
the exact voltage depends on the BOB's input circuit

if for example the BOB's input circuit is a 74HC14 CMOS IC with a 10K pull down resistor to ground
a 200 ohm pull up resistor will pull the input up to +5V



John

[Azalin]

Hi John,

The bob is a cnc4pc M16. Can I use a pull up resistor?

Sent from my MI 5s Plus using Tapatalk

[Azalin]

I don't know what a pull up resistor is but from what I understand from this video a pull up resistor is basically a resistor

Please correct me where I'm wrong. The guy on the video says

((external voltage (24 in my case)) - (target signal voltage (5v)) / R <= 5mA

I don't know what where did he get the 5mA from. Maybe it is the current value of the NPN sensor output? If so mine is 200mA. So my calculation is:

(24-5) * 200 = 3800 OHMs

Is this calculation correct?

This is the sensor by the way. In the description says the output current is 300mA but I read 200mA on mine:

https://www.aliexpress.com/item/M8-L...27424c4dih2urY

[KH0UJ]

Opto isolators also can be used if you want just to switch +5VDC on and off using GND and -24VDC trigger, if you want a simplest form just use a 24VDC mini relay to switch the 5VDC on and off

[coherent]

I went through this same issue a while back. Was a pain trying to figure out correct resistor values and wiring. Do like Khouj mentioned... its a simple, easy solution. I used a multi channel relay board. That way you can run the relays with 5 volts from your breakout board and then run 24 volts on the other side of the relay (or whatever voltage you want up to 250v) to power your NPN sensors. Really easy to wire and setup. Worked like a charm and the multi channel relay boards are very cheap on Amazon and Ebay etc. Get one with a couple extra relays and you'll be ready in case you want to add something else down the road. The relay boards have isolation and dip switches that allow you to set each relay up any way you want.

[john-100]

if the cnc4pc M16 BOB was like the C10

then you would only need to set the pull up / pull down jumper to pull up




I have only just downloaded the cnc4pc M16 manual
and its not clear what the board has fixed pull up or pull down resistors on the inputs

the RJ45 connector has 0V, +5V and 4 inputs for the limit switch kit they sell

if the cnc4pc M16 has fixed 4K7 pull up resistors
the I would expect the sensors will work with the black wire connected to the cnc4pc M16 input
and the blue wire to the cnc4pc M16 0V / GND


if the cnc4pc M16 has fixed 4K7 pull down resistors

then an external pull up resistor of 200 to 300 ohms
should over ride the effects of the 4K7 pull down resistor




John

[john-100]

Hi Azalin

I have had another look at the M16 and M8 LJ8A3-1-Z/BX data sheet

the cnc4pc M16 manual has very little detail but I expect its input circuit is going to be like the C25 BOB





looking at the data for the M8 LJ8A3-1-Z/BX sensor

it looks like the output is not an open collector output as expected as the diode( LED) and 10K resistor high lighted in the red box
provides a low current path between the positive supply and output terminal

with a 24v supply about 2mA will flow to ground via the NPN output transistor while its conducting
( if you connect a test meter set to mA across the black & blue sensor wires you should measure a 2mA current when the sensor switches off)

when the sensor switches off about 2mA will flow into the BOB input and via the IC's protection circuit to the BOB's +5V supply

a 200 ohm pullup resistor will divert some of this current and help to protect the BOB
how many sensors are you connecting to a single input ?

if you add either a 4.7V 1W zenner diode (eg 1N4732A) across the BOB input terminals

or add a diode to the input to block current from flowing into the BOB
you can use a silicon diode 1N400 to 1N4007 or a SCHOTTKY diode such as 1N5819RL has a smaller voltdrop


John