which will work with 6-36v each. I'm trying to power the receivers with a 12v 2a supply and the IR transmitters with another 12v 2a supply. Since the manual is in chinese I can't find the current draw or any other relevant info but the wiring color code schematic is fairly straight forward:
receiver has pos voltage (6-36v), gnd, and the signal which is whatever voltage is being fed to it when the beam is being received and then 0v when the beam is cut.
The ir transmitter is just pos voltage (6-36v) and gnd.
probably not the best or most efficient approach but it's the best idea i could come up with at the time.
Before I start wiring and setting up all 24 sensors, I'm trying to figure out a few things:
Is there a better approach to my board with the 24 3.3v regulators or will it likely be ok? I realize without an english datasheet for the sensors this might be hard to say.
Secondly: With 24 of these sensors on one 12v 2a supply Do you think that would be enough to provide the 24 regulators enough voltage to put out 3.3v for an arduino due?
Again, I realize since there's no datasheet, giving me a concrete answer will be more difficult but I'm looking for folks who may have used these or something similar before and might have an idea of current consumption or any other advice.
Voltage regulators are not appropriate! Use 2 resistors for each input to form a simple voltage divider. You want less than 3.3v to appear at the inputs or your board. If sensor outputs are push pull or sourcing your good to go.
If sensor outputs sink only set your board inputs as input pullups no resistors are needed.
Measure the current draw for one transmitter and one receiver X 24 for each plus some extra ma for the resistor networks will give you the size of the 12v supply. Might want a 9v or 6v if you have to order a new one.
Good idea on measuring the current on just one. (i'm not super confident on my multimeter's ability to measure current, it seems like it's been way off before but i'll give it a go) OK. 10mA a piece.
I did consider using voltage divider circuits but I was unsure how it would scale on 24, I was worried about fluctuations. It seems like the voltage drop is somewhat heavy (like 1 or two volts) when only 6 are powered up and I'm also not sure how it would react to multiple sensors being triggered at once which seems like it might raise the voltage a bit?
To complicate matters, all of these sensors are already installed on stairs at a busy children's science museum that's only closed once a week and it's an unpaid volunteer project so staying there for more than a few hours to experiment on a monday is proving to be another challenge.
I was hoping someone knew of an ic sort of like a max232 level shifter/converter that had 4-8 in and outs. I've looked a bit through forums but i haven't found any that have more than one i/o yet.
What's your opposition to the regulators, Ray? too slow and inefficient?
Are you saying your power supply is dropping several volts when you power out 6 of these?? Somethings not right there check your wiring. Sounds like your using a lot more than 10ma each.
You could use an opto coupler with transistor output and will provide complete isolation.
In the eBay listing it seems to indicate 300mA, whether that is current draw or current passing of the switch I can't be sure. The attached image seems to show something that looks like 300mA on the two parts.
You're right, it does say 300mA. I'm thinking that part of my multimeter might actually be damaged by high current one time. I just tried it with a cheaper one i had that wasn't presumably blown and i'm getting 210mA
it surprises me that the receiver would draw that much current, but i guess that makes sense now. I guess that also explains the voltage drop
The transmitter is likely 300ma max and the receiver would switch 300ma max. The circuitry in the receiver might use 10-20ma too. If going with optos you'll be switching 10ma.
I used two different methods to try measuring the current. for the 10mA i got the first time i wired the meter's com to the power supply's positive then the 10adc lead to the receiver's positive, the power supply's ground was connected to the receiver's negative.
I believe this is the correct way to measure current
I was getting 210mA by connecting the meter's probes directly to the positive and negative power supply leads connected directly to the receiver's + and -
would it probably be safe then to assume that the receivers use 10mA each when not switching then (up to?) 300mA when switched?
so i should then get a power supply rated for 300-310mA x 24?
I'm guessing that the sensor has an internal 10K pullup resistor (I've seen this on other similar sensor types). Powering it with 12V and trying to achieve 3.3V output voltage, I would definitely use a resistive voltage divider. Try connecting a 3.6K resistor from the NPN output to GND and see if the output voltage switches from 3.2V to near 0V. Note that 300mA current rating would be the rating of the internal NPN transistor. The Arduino Due's inputs would be protected by internal protection diodes ... you'll have no problems if you make sure this current is <= 1mA. Therefore, if the sensor has an internal 10K pullup, then the output could be directly connected to the Due and the protection diode current would be (12-3.3)/10K = 0.87mA. However I recommend using the 3.6K pulldown as described earlier. Please test the output voltage with the NPN on and off prior to making connection to the Due.
