shiftBrite issues

I'm trying to create some lights to go round a garden pond. I've got 31 shiftBrites wired up with power being injected every 4 units and at the end of the chain. It's powered by a regulated switchable power supply that can supply up to 4A. I'm pretty sure the grounds are tied together as I've built a small board to step the power down to 5v to supply the Arduino Pro Mini I'm using to control them and it also passes the input voltage straight to the lights as well.

With the power supply connected directly to the lights and Arduino all is fine at 5v. However if I increase the voltage of the supply up to 6 or 7v the shiftBrites start flickering like mad and bear no resemblance to what they are supposed to be doing.

Can anyone point me in the right direction as to where I may be going wrong? I ask because I need to extend the connections to the lights so they can be outside and the control box inside a garage. At the moment I've got a 4m cable made up and again at 5v it works ok (with some flickering on the lights at the end of the chain) and would like to up the voltage for more stability.

Thanks in advance :wink:

How long are the cables between the ShiftBrites? Also, are you extra sure the grounds are solidly connected? Can you link to the supply you're using?

4 meters is usually too far for any kind of TTL signal. However I have a report from someone in Australia who succeeded with ShiftBrites on a long cable by using CAT5 and putting a data wire + ground on each pair, then running a separate power cable alongside.

The cables between the shiftBrites are roughly 30cm each.

Here's a link to the power supply :- http://www.maplin.co.uk/Module.aspx?ModuleNo=48517

That page says it delivers 4A but the back of the unit says 5A between 5 & 12V

I've got a small regulator circuit to step the power down for the Arduino Pro Mini that uses a 7805 regulator. The power and gnd for the lights comes out one end and the power and gnd for the arduino come out the other.

The cable can probably be shorter but I wanted to start at 4m and see how that went. At 5V it's almost there. I'm using your fadeTo routines and the SPI code and at full red, green or blue there's a slight flicker. Full white causes a bit of madness towards the end of the chain. On the other colours it's only the end of the chain (last 3 or 4) that has a problem which made me think it was a power issue as the signal seems to be getting to most of them fine. Am I right in thinking that each shiftBrite essentially acts as a relay for the signal?

Each module does buffer the logic signals to the next device.

Raising voltage should increase stability, not reduce it...unless the low voltage is limiting the available current.

Let's try a short cable to the first Shiftbrite and see if that improves performance. At least we can identify or eliminate that factor.

I did have it directly connected to the Arduino before adding the large cable. Like now it was stable at 5v (admittedly more stable than now) but at anything higher went mental.

For reference here's the regulator circuit I'm using.

It's laid out on stripboard and physically pretty much matches the diagram above. I've measured the voltages at each end and with a 7.5v input I get that on the input side and 5v on the output side, so all seems to be working as it should.

I'm not to bad with the programming side of things but quite new to the whole electronics thing (I know, i hide it well :P), so this has me quite confused.

If you really have a Pro Mini, there should already be a regulator on board. You could connect the 7.5V directly to the RAW power input. Do you know if you have the 5V or 3.3V version of the Mini?

I saw that yesterday looking at the board specs, d'oh (_8(!)

I've got the 5v version.

Tried removing my regulator and going straight into raw input last night, it's getting better but now I think it's down to the cable length as you mentioned before. Even taking it down to the minimum I can have (2m) it's still a bit stroppy.

I'm off to get some network cable tonight and give that a whirl. Do you know what sort of length the chap from Oz was using?

Many thanks for all your input btw and for a great product. ;D

It was a pretty long cable, something like 10m. I was surprised it worked at all, but he claims setting it up as twisted pair with ground, it was flawless.

You may want to try adding some large capacitors to the LED supply rail. Not all supplies are created equal, some might dip significantly with the type of sudden high current spikes that PWM circuits generate.