sweevo Posted July 20, 2009 Share Posted July 20, 2009 Just finished all the coding for my RTC and LCD display for my DIY LED Rig. Only problem I've got now is that i've not got enough digital output pins to be able to drive it, the cooling fans AND the six buckpucks all off seperate digital I/O pins. I wondered if anyone had tried to control 2 or 3 buckoucks using PWM from a single I/O pin on an Arduino/ATMega ? I know the max current for an I/O pin is 40mA, also the input impedance of the Buckpuck CTL pin is listed as 1K. Not sure if Ohms law can be applied here but I make the current required to drive one CTL pin 5mA, ie 5V/1000ohms. If all this is correct then driving 3 CTL pins would only require 15mA which is well within the 40mA limit. Anyone tried controlling more than one Buckpuck like this? Link to comment
evilc66 Posted July 20, 2009 Share Posted July 20, 2009 Use a transistor at each Buckpuck with a biasing resistor and tie them all to a single I/O pin. Link to comment
sweevo Posted July 20, 2009 Author Share Posted July 20, 2009 Thought you might be the man to know. Could using an optocoupler (CNY75) in the same manner work? Just trying to keep it simpler/tidy. Link to comment
evilc66 Posted July 20, 2009 Share Posted July 20, 2009 Wouldn't bother. A transistor is cheap and will work just fine. Optocouplers are great if you are looking to isolate the signal line, but not if you are needing to use a different current source. Link to comment
sweevo Posted July 21, 2009 Author Share Posted July 21, 2009 Wouldn't bother. A transistor is cheap and will work just fine. Optocouplers are great if you are looking to isolate the signal line, but not if you are needing to use a different current source. Ok, had a look at wiring diagrams (fig14) in the datasheet for the Buckpucks. They've got a 2N4403 (PNP) wired up to the CTL and 5V Ref pins. Can you explain which way I should I wire up the biasing resistor and PWM signal coming into the base please? I thought the PWM signal would need to be 0.7V before the transistor would switch you see. Link to comment
isidro0 Posted July 21, 2009 Share Posted July 21, 2009 I've ran 4 drivers off 1 pwm pin without any problems so far, about 1 year.(atmega644) Link to comment
sweevo Posted July 21, 2009 Author Share Posted July 21, 2009 I've ran 4 drivers off 1 pwm pin without any problems so far, about 1 year.(atmega644) The ATMega I've got is a 168, not sure if there's much difference in terms of drive current. What LED drivers did you use, buckpucks too? Link to comment
isidro0 Posted July 22, 2009 Share Posted July 22, 2009 Currently im using some from sure-electronics, I think when I fist started i ran 7 drivers from one pin, including lm317 drivers. Just order an extra chip just in case, which you should have an extra anyways. Link to comment
evilc66 Posted July 22, 2009 Share Posted July 22, 2009 For the cost of a transistor, it's not worth risking cooking the output pin. Connect a transistor like this +5v +5v +5v | | | / / / -| -| -| | \ | \ | \ R | R | R | | BP | BP | BP | | |ARDUINO------------------ Sorry for the horrible diagram. R is something like a 5K or 10K resistor. Use an NPN transistor and connect the +5v (you can use the Buckpuck reference voltage) to the collector and the Buckpuck CTRL pin to the emitter. Link to comment
sweevo Posted July 22, 2009 Author Share Posted July 22, 2009 Thanks for the diagram, it's a great help. Need to read up on biasing transistors as this the point where I look at circuit diagrams and go pale. Think I got a few transistors stashed away in my box of all things electronics. I'll have a rummage tonight. Link to comment
spark Posted September 4, 2009 Share Posted September 4, 2009 This should work... It is a biasing transistor that basically just has the resistor built in. Same specs as the PNP shown in the BuckPuck sheet, but with a 4.7K resistor built in on the base. FJN3309R.pdf Link to comment
nickijon Posted May 24, 2010 Share Posted May 24, 2010 Use an NPN transistor and connect the +5v (you can use the Buckpuck reference voltage) to the collector and the Buckpuck CTRL pin to the emitter. Shouldn't PNP be the correct one? Not NPN? Same specs as the PNP shown in the BuckPuck sheet, but with a 4.7K resistor built in on the base. I did some additional digging in other threads, datasheets, and regarding the FJN3309R. I think you're actually thinking about the complement to the 3309, that is, the FJN4309R. The PNP is the one that looks to match the transistor in LedDynamic's datasheet, fig. 12. PNP Transistor with 4.7k Ohm Bias built-in http://www.fairchildsemi.com/ds/FJ/FJN4309R.pdf Hope I'm seeing this correctly. Hope this helps. Link to comment
sialkoti Posted May 24, 2010 Share Posted May 24, 2010 Nice to see such a great and old thread to come back alive Link to comment
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