Powering the Spark from 12v

I’m designing an LED strip controller including the Spark. When I’ve done something similar from an Arduino I’ve taken the 12v PSU and split off a channel via a 7805 to power the Arduino via the same PSU as the LED strip.

As the Spark runs at 3.3v, I don’t like the thought of the heat a regulator (e.g. LM1117T) would put out to drop from 12v.

I’m thinking of sticking with the 7805 (or a UBEC but they’re a bit big) and using that as input to the VIN/RAW pin1 which I understand has a 3.3v regulator that can take up to 6v as input and output 3.3v on VCC (what’s 3.3v with the dot?) what i don’t like about that is that all my current would have to flow through the Spark, esentially the Spark is an expensive 5v-3.3v regulator!

I’m going to use 3 STP16NF06L logic level MOSFETs to control the PWM signal to the LED strip RGB channels, but other than that, there’s not going to be [m]any other components, maybe an LDR or PIR or capacitive touch sensor.

What are the power requirements of the Spark when using wifi - 350mA max. I think i saw somewhere? As I could use one of these 600mA or these 500mA Pololu bucks if I can keep current consumption down. Oooh, the TSR 1-2433’s look quite nice at 1A too…

I don’t want to use USB power or a shield or a breadboard PSU or anything so big as one of those LM2596 boards you get on ebay. So what kind of thing are people doing to get 3.3v?

The alternative is to switch to WS2182 LED strips which can run from a 5v PSU which is easier to regulate, but I’ve already got 5m of analogue 12v strip which is cheaper than 1m of digital.

sej​7278, regulating 12v down to 5v with a 7805 will create a lot of heat due to the 7v drop and the maximum 350ma consumed by the CC3000. Your idea of using the bucks is much better and if your sensors are not too power hungry, the 500ma Polulu is fine. However, I agree the TSR 1-2433 looks really good! I use a Polulu 500ma buck on one of my projects.

The 3.3v* pin is a filtered 3.3v pin originally intended for powering noise sensitive sensors.

I agree that it makes no sense to buy individually addressable LEDs if you already have analog ones though that is really dependent on what you doing.

Keep me posted on you project :smile:

I have never been big on putting two linear regulators in series. It is like having two control loops that can fight each other. Another alternative is a two-output PSU, one for the analog LEDs and one for the core. PC power supplies are remarkable cheap these days.

I would not change the LED strips if you have them already. The real advantage the WS2182 strips is individual addressability which I assume you are giving up with the analog strips. In the analog ones fit your project they are a lot cheaper.

Thanks for the responses, no I won’t be getting new digital strips until I need individual addressability e.g. for Boblight, they’re still absurdly expensive ($15/metre is cheapest I can find).

No I don’t really want to use two LDO’s in series or cope with 2.5w of heat from that 7v drop!

Those TSR’s are very sexy, can’t find many distributors though. So if I used a TSR or Pololu, as they’re regulated 3.3v I’d connect them to 3.3v* rather than VIN to bypass the reg (via a smoothing cap or somesuch)?

Hi @sej7278

I think you can back-drive the core 3.3V pins (not 3v3* which is filtered for the ADC reference) as long as you don’t connect to VIN or the USB power.

yup, similar to the arduino’s - don’t plug into usb or dc jack whilst powering via a pin!

i’ve found these tiny bucks and these slightly larger ones that have an extra diode/rectifier for 99p on ebay, so have ordered some to play with, not so keen on setting the Vout via a pot though!

Those chips look great. For my lights i am using the following

12v led driver
12v to 5v drop down converter. The sort for cars

But those chips would be much smaller. And a very good price

oh you’re taking a cigarette lighter usb charger apart or something are you?

No i got it on ebay. Its a 12v to 5v converter. Just 2 wires for 12v but it has a micro usb connector on the other side, so it plugs directly into the spark

basically one of these, but with a micro usb connector on the end

ah yes i almost bought a 3.3v version of one of those (not with usb on the end) but i thought it would be too big

My led controller is just white, so for me i am going to get a pcb mount 5v supply, wire it to vin, and then control the fet. Trying to make the entire thing fit on the back of a 12v led driver. So about 40x80mm which should be pretty easy

my two arrived today, the smaller ones (super mini) are better as the big one (just mini) is pretty hard to adjust - the pot needs really small turns and there’s no way you’d ever get exactly 3.3v, i managed 3.34v which should be fine.

unfortunately none of them fit breadboard/veroboard, so i’ll have to solder wires to them instead of header pins.

@sej​7278, great info on those modules! Keep us posted on how well they work :smile: