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Will this circuit work like I think it will?

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JimmyG1976

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Hello all! First post for me here. So a little background on what I'm trying to do. I work in the industrial electrical field and electronics is not my specialty, although I'm learning new things all the time. What I want this circuit to do is 3 things:

1. a portable 24vdc power supply for very low current applications.

2. using J5, be able to plug a PNP/NPN sensor into it and get a visual indicator that the sensor is powering on and the PNP/NPN outputs are functioning.

3. Using J's 1-4, be able to plug in the wires from those sensors (some don't have detachable cables) and do the same thing in 1. but have the LED's change color depending on whether J3 and J4 are negative out (NPN) or positive out (PNP) So J1 and J2 would supply voltage to the sensor and J3 and J4 mirror each other but depending on polarity light up a different color.

I know I could accomplish the same thing with a couple of 2 pole bi-color LEDs, a couple 1k resistors and 3 9v batteries, but the purpose of this little project is for two things. Giving my technicians a tool to easily troubleshoot whether a cable is bad or the sensor is bad and hopefully they learn a little while they build their own.

Some information on the types of sensors we use are most all will operate from 10-30vdc, types are usually inductive or photo-electric.

So will it work like I want it to? And what if I wanted to use common cathode RGB LED's instead. My knowledge on diodes is limited and in my head it works but unfortunately real life and what's going on upstairs don't always coincide.


tester_V1.JPG
 

betwixt

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That isn't the conventional way of drawing a schematic but I think it might work. I'm not sure exactly what you expect it to do though, under what conditions do you expect the LEDs to operate?

The resistor values are highly suspicious, you have R1 at R360 (= 0.36 Ohms) when it probably wants to be 1K or so. Similarly, if U1 is producing 48V and you are testing 'straight through' cables the LEDs will be passing over 40mA which is probably excessive and would equate to around 200mA load from the battery per LED. Even if U1 is producing 24V across its output the current will still be too high. You should start by defining the LED current you need and recalculate the resistor values.

Brian.
 

KlausST

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Hi,

I agree. It may work, but some functions not like you expect.

the naming of your DCDC converter is misleading. +24V and -24V give a total of 48V. But I guess it is a simple 24V DC output.
Usually one calls one ouput "GND" or "0V" and the other "+24V".

in case you have a small 9V battery ... it will soon be drained out.

I guess the value of R1 should be "360" or "360R" which means 360 Ohms. With this you get about 25mA of LED current when battery is full (9V is nominal voltage. It will be a little more when the battery is new and it will drop down to maybe 7.5V when it is considered empty.
Usual LEDs should be driven with current below 20mA. Don´t go to the limits. They will be happy with 5mA, too. While the battery will be alive 5 times longer. (ignoring other currents)

J1, J2, J4 are identical to the connections of the sensor connector J5. Are you sure J3 is different?

What you might not expect:
The dual LEDs are ON all the time (sensor disconnected, broken sensor wire, inactive sensor output) .. because they are wired in series. They will see half the current...but you hardly will be able to recognize whether a LED is driven with 10mA or 20mA.
And one LED goes OFF when a sensor output is activated.

For a simple tool this will work. And it´s good for learning. See it as electronics development. It will do something useful, but there will be steps to optimize.

Some hints for improvement:
* reduce battery current when sensor is disconnected for the battery to live longer.
* add some transistors so that the LEDS are OFF all the time, and only one is ON when the sensor output is activated.
* auto power OFF
* short circuit protection. In case a sensor is defective, wrongly wired, or cabling has short circuit.

Klaus
 

JimmyG1976

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I appreciate your feedback. I'm taking your guys advice and using the highest value resistors I can to save on battery. Yes J3 is the same. I saw that. I've also run into some problems prototyping this. I'm stuck using RGB cathode common LED's and I'm really not sure how to make it work. We have 3 main types of sensors. The cables are pretty much universal. Brown wire 24vdc and blue 0vdc this powers the sensor. Then black is always 24vdc signal. The white wire is where it gets tricky. It can be ground in an NPN sensor, 24vdc in a NO/NC PNP sensor, or nothing at all. So there is need for short circuit protection when using J5. I just can't see a way to make both LED's do the same thing regardless of which wire is plugged into J3 and J4. Maybe I just need J3 and J4 to act as two separate channels with a diode or two for protection. Anyone have any thoughts?
 

tonaleva12

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Batter for sure will be beneficial while you used highest value resistors
 

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