MK120 Light barrier from 12V DC power supply

[smilem]

I have MK120 Light barrier and it works fine, I would like to run it from 12V DC power supply. **broken link removed**

These are given specs:
transmitter emitter: 9Vdc, 50ma max.
receiver detector: 9Vdc, 20ma max

So to run at 9V DC I need to add 43 Ohms resistor in series to get 9V from 12V?
Or can I run them from 12V directly?
Or perhaps it's better to change some resistors on PCB, if so what components needs to be changed?

Here is light source schematic: http://www.velleman.eu/downloads/files/schema/transmitter.jpg
Here is sensor schematic: http://www.velleman.eu/downloads/files/schema/receiver.jpg



Thank you.

 

[Reloadron]

I have MK120 Light barrier and it works fine, I would like to run it from 12V DC power supply. **broken link removed**

These are given specs:
transmitter emitter: 9Vdc, 50ma max.
receiver detector: 9Vdc, 20ma max

So to run at 9V DC I need to add 43 Ohms resistor in series to get 9V from 12V?
Or can I run them from 12V directly?
Or perhaps it's better to change some resistors on PCB, if so what components needs to be changed?

Here is light source schematic: http://www.velleman.eu/downloads/files/schema/transmitter.jpg
Here is sensor schematic: http://www.velleman.eu/downloads/files/schema/receiver.jpg



Thank you.

The currents listed are maximum values, the actual current used will vary on what the circuits are doing. That precludes just placing a resistor in series to drop 12 to 9 volts and run the units.

Note that on each circuit there is a 1N4007 diode in series with the power. That diode will drop about .6 volt leading me to believe the actual circuits run on less athn 9 volts and more like 8.4 volts approximately.

Changing resistors really isn't practical for both boards.

My choice would be to use a few LM7809 regulators to give you 9 volts from a 12 volt source. The data sheet can be found here. That is how I would likely go about it.

Ron

 

[smilem]

Thanks for you suggestion, I use LM338 as voltage regulator (see picture) now and since it gets very hot I was thinking to use 12V somehow. My main voltage used by this project is 12V for motor, LED etc. Only this circuit needs 9V.

I was thinking to drop the LM338 PSU and get something like this
**broken link removed**

Should be enough for all my stuff:

LED is 3W
IR is 100mA
Motor about 25W

And I still got 7W unused.
I'm planning to move my stuff to new case and it will be convection cooled only, so I'm worried about heat problems and instability.

I also have another question:
I have made dual PSU to reduce noise from motor circuit (with PWM driver) to the LED circuit (another LM338T constant curren circuit). Or perhaps they can share same PSU without any issues?

Thanks.

 

[Reloadron]

25 watt motor @ 12 volts is a little over 2 amps so keep that in mind. As to noise the separate PSU is a good idea but I would try a cap across the motor terminals also (about .1 uF). I was only looking at the transmitter and receiver and had no idea there was a 2 amp motor involved when suggesting the LM7809 regulators. Nice little dual PSU by the way.

Ron