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Old 5th May 2015, 8:45 PM   #1
oculi Thread Starter
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Default stupid question, will my ULN2803 circuit work?

Hi all,

Like everyone I have long dreamed of switching 12 volt loads with an arduino (or your choice of micro/low voltage signal)

will this circuit using a ULN2803 work?



and by work I mean will the globe light up when I send 5 volts out of the output of the ardunio? (the globe is a special globe which will only light up when ~10 volts goes through it)

took me a while to remember that the symbol in the IV is just a not gate, and the diodes are for flyback, which is handy because i don;t need to remember which way to hook them up externally.
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Old 5th May 2015, 9:02 PM   #2
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Yeah looks good, but those ULN2803 are only good for 80mA or so so be carefull. You might want to parallel up several channels if it requires more current than that.

Alternatively if you only have a single load, try to get the hang of a low side N type mosfet drive. Very simple circuit and easy to drive with logic level mosfets.
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Old 5th May 2015, 9:14 PM   #3
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Quote:
Originally Posted by aXis View Post
Yeah looks good, but those ULN2803 are only good for 80mA or so so be carefull. You might want to parallel up several channels if it requires more current than that.

Alternatively if you only have a single load, try to get the hang of a low side N type mosfet drive. Very simple circuit and easy to drive with logic level mosfets.
cheers, I need the voltage more than the current, will be using it to drive a relay maybe which it should do easily.
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Old 6th May 2015, 9:31 AM   #4
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Just curious, is the relay then driving a high voltage circuit, or is it still 12V?
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Old 6th May 2015, 11:56 AM   #5
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A much better IC is TPIC6B595 this is a serial in parallele out shift register with 8 FET outputs you only need 3 pins of the Arduino to get as many outputs as you want.
Has high current outputs of 150ma per output with all outputs on, made to drive relays.
With these you can get more outputs just by adding more TPIC6B595 in series.
They are high power versions of 74HC595 which you will find easy to use with Arduino
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Old 6th May 2015, 1:34 PM   #6
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Quote:
Originally Posted by aXis View Post
Yeah looks good, but those ULN2803 are only good for 80mA or so so be carefull. You might want to parallel up several channels if it requires more current than that.
http://www.ti.com/lit/ds/symlink/uln2803a.pdf

500mA sink per output, total current 2.5A. We used zillions of them to drive lamps.
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Old 6th May 2015, 1:46 PM   #7
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Sorry, my mistake. I used one couple of months ago and thought I had remembered the specs.
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Old 10th May 2015, 9:13 PM   #8
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Quote:
Originally Posted by aXis View Post
Just curious, is the relay then driving a high voltage circuit, or is it still 12V?
the relay (when/if used) will be switching ~12 volt loads

Quote:
Originally Posted by paulvk View Post
A much better IC is TPIC6B595 this is a serial in parallele out shift register with 8 FET outputs you only need 3 pins of the Arduino to get as many outputs as you want.
Has high current outputs of 150ma per output with all outputs on, made to drive relays.
With these you can get more outputs just by adding more TPIC6B595 in series.
They are high power versions of 74HC595 which you will find easy to use with Arduino
cheers for that, may look at them in the future, only looking to control a few things at the moment and I don't mind using all of the output pins for that.
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Old 11th May 2015, 12:58 AM   #9
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damn, wish i'd known about this for my current project... 70 relays controlled by individual FETs with flyback relays mounted on each relay...

oh well...

How many outputs from the Arduino do you need? You might need to look at current limiting resistors on the outputs?
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Old 16th May 2015, 11:53 PM   #10
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wired this up, works great on the relays!
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Old 22nd May 2015, 9:12 PM   #11
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I just bought a relay board on ebay (I will be using it for other than arduino purposes). It appears to even have opto isolator whatsits and they are cheap. Search for relay board ardunio.
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Old 22nd May 2015, 9:18 PM   #12
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Quote:
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I just bought a relay board on ebay (I will be using it for other than arduino purposes). It appears to even have opto isolator whatsits and they are cheap. Search for relay board ardunio.
yep that's a good way to do relays, and pretty cheap too. will probably go down that road for certain projects, but my circuit above will work well for multiplexing too (for large 7 segment displays etc) you can probably do that with relays but they won't last very long
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Old 22nd May 2015, 10:21 PM   #13
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Cool. FWIW I think there are solid state relay versions too.
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