7 replies to this topic

[perkunas]

I would like to know the max load for the on board 5volt supply (I guess the wall wart 1 or 2 amp would have to affect things) I keep adding things to my netduino, I`m scared I`m going to over load it.

[JerseyTechGuy]

Max I believe is 200 mA total.

[Stefan]

Max I believe is 200 mA total.

Indeed. Also, per pin are some specific specs: http://www.netduino....duino/specs.htm

[Geancarlo2]

200mA is the maximum ammount of current the microcontroller I/Os can draw(Page 14 http://www.atmel.com/Images/6120s.pdf) The maximum current on the 5V rail depends on what voltage you are feeding the board with, but in general you should be ok with up to 800 mA. It pretty much depends if you are able to sink the heat dissipated.(http://www.onsemi.co...l/MC33269-D.PDF)

[perkunas]

Thanks the reason I'm asking this, is because I'm using optical relays, and it has a warning Quote "NOTE: Each relay draws about .08A (80 Ma) when on, so if all 8 relays are actuated the board needs about 8*80 or 640 Ma (.64 amps). In this case a separate power supply for the relay board is required. Connect as in preceeding paragraph. A 5 Volt 1 A supply would be good." and "actuate more than 3 or 4 relays at once, connect Arduino +5 separate power supply" Its not an arduino its netduino I'm using 5 relays at once, and have two input ports controlling them. I don't want to use a separate power supply if I don't have to so 5 X 80 = 400MA plus a little for loss and the input ports I think I should be OK maybe IDK

[JerseyTechGuy]

When I build SSR boards for these kind of purposes I usually have then powered by a separate power supply. I learned this the hard way running a bunch of animated christmas lights.

[carb]

Perkunas, There are several current limits that you need to watch. The most limiting is the per pin current rating. From the Netduino Hardware Specs on Netduino Hardware Page of Netduino.com: max current: 8 mA per pin digital pins 2, 3, 7: 16 mA per pin analog pins 0-3: 2 mA per pin microcontroller max current: 200 mA total The current draw for the optical isolators will exceed the pin limits unless you use a transistor between the optical isolator and the IO pin. The limit for the onboard regulators is 800 milli-amps, but I personnaly don't like to exceed about 50% of that unless I have good heat sinks or fan to help maintain the temperature of the regulators. Also picking a power source that has a voltage that is close to the 5 vdc output helps (7.5 to 9 vdc) the heat produced by dropping the extra voltage is less the closer you are between the input and outputs (heat or power loss = current x voltage drop regulator for Liner Voltage Regulators). If you want more information on the onboard voltage regulators, go to the hardware page for the Netduino, open the schematic drawing, lookup the part number for the 5 vdc regulator (or 3.3) and google it (MC33269DT-5.0G or MC33269DT-3.3G), you should be able to find a data sheet. I agree with Dave and reccommend a separate power supply to drive the relays, either mechanical or solid state. Hope this helps, Chuck

[terb]

If you need more power from your outputs, I guess you could easyly buffer them with a transistor wired in follower. the current available will then be dependant of the transistor you choose, but it will easyly be way higher than what the Netduino can provide. The basic thing is really easy to do even for a beginner in electronic : http://upload.wikime...ollower.svg.png For more, see the "Emitter-Follower Buffer" paragraher : http://hyperphysics....ic/emitfol.html