Heavy Load Switching with CodeBug

Not yet, but I'm almost sure it works. I have used a PN2222 to manage high load with a 3V on a PI so why not ?

At the risk of a certain intervention ...

http://www.itead.cc/electronic-brick-5v-relay.html?___SID=U

http://www.itead.cc/2-channels-5v-relay-module.html?___SID=U

If you check the wiki they include a transistor driving the relay.

The other thought is Terry King has optocoupled units.

http://yourduino.com/sunshop2/index.php?l=product_detail&p=218

Mark

The 'GPIO Explained' schematic with the transistor and relay should work too.

(For some reason the editor is mangling the URL - will raise a feedback & support request. Circuit is below):

(Finder 32.21.7.005.2000Finder 32.21.7.005.2000 is a convenient relay for up to 6A, fits stripboard nicely).

Or a MOSFET based circuit, but I left them out of GPIO Explained due to opportunities to go wrong if people attempt to use alternatives!),

A MOSFET like this would do you (assuming that your load is operating from a voltage less than 20V)

http://uk.farnell.com/taiwan-semiconductor/tsm2312cx/mosfet-n-ch-20v-4-9a-sot23/dp/1864587

The Vbe threshold is low enough that the 3V CodeBug outputs will switch it. The on resistance is only 27mOhms, so even at 3A it only has to dissipate a quarter of a watt (0.243W) which the package alone should manage.

Connect the gate to the CodeBug output, the source to GND, and the drain to your load (with the other side of the load connected to the supply you're using). Remember to connect the ground of the CodeBug and the ground of the load power supply together.

If the load is inductive (coil of some sort) include a catching diode as per the transistor circuit in shabaz's post.

Observe static precautions handling the transistor before you get it wired in the circuit.

If you want to prevent it turning on and off  before the CodeBug initialises its output pin ("flapping around" to use the technical term), include a resistor from the gate down to ground to keep the MOSFET turned off until it is actually being properly driven by the output.

If you decide to take this approach, let us all know how you get on.

Ah, nice! I was just this moment looking at an AOT460 MOSFET for the same purpose, Jon -- but the one you suggested looks preferable (cheaper, too!). Excellent suggestion, and thanks for the setup description.

Excellent suggestion, Shabaz, and I'm now wondering whether to go with Jon's MOSFET option, or whether to get a double pole relay and switch both loads from just one of the CodeBug's legs. Although I may need to control them separately... I'll have to think about that some more

Either way, always appreciate the ideas from all your guys!

Hi Spanner,

Personally I'd go with Jon's suggestion for my own boards, only caveat is that it is a surface mount device which not everyone is comfortable with. If you're using a relay, then you may as well use the NPN method, since it doesn't care what specific NPN transistor you use.

But yes, many ways to swing a cat : )

Absolutely. And there may be real advantages to having the isolation that the relay gives; without knowing a bit more about what "Spanner Spencer" is trying to do it's difficult to say.

The bipolar transistor is much more robust handling-wise, too, particularly if poeple aren't used to electronics and don't understand about the possibility of static damage.

Soldering an SOT23 is quite easy, though. They're probably the easiest SMD parts to prototype with (at least I can see the things, which isn't the case with some of the surface mount resistors you can get now).

Oh John, you're such an optimist

I read the same data sheet and come away with 40 - 50 mOhms (40 @ 2.5V gate drive + about 30% for being hot).

But still good for 3A (just about at ambient = 25)

MK

Mea culpa!

It was staring me in the face right at the top, too. But he/she did only ask for 1 to 2A, and the typical rds-on would be a bit better, and I presume this is experimenting and hacking rather than straight product design, so I think we'd get away with it. But you're right, it doesn't set a particularly good example.

Curiously, by nature, I'm a right old pessimist.

BTW Your post really confused me at first (calling me John) because when I'm logged in I see my real name (Jonathan) above my posts and I presumed that was what everyone else saw too. What an odd system.