Any old clocks ?

[electrokid]

The bulb in my clock has gone again so it's time to get off my fat backside and actually get on and do the project I intended to do last time it went - a properly controlled LED illuminator.

Control of the brightness of an LED is not as straighforward as with the standard bulb - it'll have to have reasonably accurate current control - and it would be silly to do the design work and not offer it to everyone else - so I want to set up a jig.

What I'm after altogether is - a clock obviously - but also some length of the cable loom up to the connector (so I can build that into my jig and just plug another BX clock in as needed). I'm also after the tray that the clock is attached to (there may be some adjustment pots which could be fitted into the tray).

Mat is sending me a duff clock which is helpful - if you have any duff clocks you'd like to send I'll have a look to see if they are fixable - I'm going to need at least one working one but that could easily be a duff one I've fixed.

Any offers ?

[Mike E (uk)]

There are lots of purpose made LED brightness controllers around,but simply controlling the current with a linear or switching regulator works very well unless you want to get the LEDs very dim,when balancing the light output from multiple LEDs becomes problematic.

[electrokid]

Yes Mike - it's not a problem but I'd like to get something 'universal' implemented. I've done a fair amount of work recently on LED drivers (including light output control of tri-colour LEDs in series ) so it's all quite fresh in my mind etc.

I'm currently thinking of using a single tri-colour LED with the brighness not only modulated by lights on / lights / off but also by ambient light. I'll look for a 5mm tri-colour LED - the only Tri-colour LEDs I have in stock at the moment are 10mm but the light output from these is definitely adequate if I can get it in the housing.

The 'standard' 20mA LEDs are more efficient (light output per watt) than the higher wattage devices and last much longer so that's what I'll use - and the LM317T reg is cheap and completely bulletproof if reverse current protection diodes are fitted.

Using a 3 colour LED it could even be set up to change colour when the lights are switched on !

[Mike E (uk)]

Agreed it would be nice to have it dimmed with the dash light dimming control
If making the dimming automatic, I would control all the dash lights, but have them all switched off when the cars lights are off, as they are at the moment if you have changed the feed so you don't drive off in a brightly lit area at night without headlamps on.
Y

[mat_fenwick]

Pretty sure I have some 5mm tri-colours; I'll pop a few in with the clock as realistically I'm not going to do anything with them!

[electrokid]

Agreed it would be nice to have it dimmed with the dash light dimming control

That's an idea I hadn't considered - I'll see if it's useful to include that. The clock is outside the normal view so it's a 'glance and check' process that doesn't perhaps need the same level of control as the main dash lights - we'll see. I personally don't have any issues with the dash lights being on all the time but I can see how changing that could be useful.

Pretty sure I have some 5mm tri-colours; I'll pop a few in with the clock as realistically I'm not going to do anything with them!

Thanks Mat - much appreciated. I'm currently looking at these...


http://www.ebay.co.uk/itm/350364203554? ... 1438.l2649

and these...

http://www.ebay.co.uk/itm/370280090959? ... 1438.l2649

which seem to have the highest output for a 5mm tri-led - 8000 mcd and compare favourably with the 10mm I have in stock which are red, 8 to 12 Kmcd, green 20 to 24 Kmcd, blue 16 to 20 Kmcd and from a supplier I've used before and is a known quantity. I'll fit the 10mm though if there's the space to do so. Also the price is right - £18 used to be the cut-off point below which customs and excise didn't bother but now anything imported between £15 and £18 attracts VAT and so also goes through the 'red channel'. Anything that attracts duty and / or VAT I have to collect - usually from Aldershot (10 miles) and also pay the post office charge of £8 for 'handling'. So it's a good idea to keep under the £15.

The intention is to publish the design and offer the mod as a service at mates rates - but it will need to be a plug-in replacement hence the need of a small chunk of the loom and the connector to make a jig.

[mat_fenwick]

I've found the RGB LEDs now, so will send them off. No voltage or current information though, so you might have to guesstimate. Would have thought 30 mA would do without running any risk.

Just one point though - would it be better to select LEDs based on a lumen rating rather than candela? As the latter is a measure of peak beam intensity rather than overall output, so a narrow angle beam (not what you want for clock illumination) would have a higher cd rating than a wide angle LED of identical output.

[electrokid]

Thanks for that Mat

No guesstimation needed though - practically all small LED junctions are built to run at 20mA continuous / 100mA max pulsed though they can be overrun at 25 or 30mA that is likely to reduce their life - as will running them in pulse mode as the mark / space ratio gets closer to 20% - running greater than 20% at 100mA will shorten their life considerably. However if they are run at the designed 20mA then they virtually last for ever unless you're very very unlucky. On the stuff I've built over the years I've never had an LED fail.

LED outputs are specified in mcd these days - it's what we're stuck with and although there are some wide beam versions (with correspondingly lower mcd rated outputs of course) they all throw the light forwards from the device which is not at all what the bulb does. There are also diffused versions but AFAIK they still produce a prominent main lobe forwards with very little at the side...

which is why I intend to add reflectors and diffusion as appropriate.

One thing that works very well as a diffuser is the glass beads that are used on numberplates. In front of the white or yellow paint on numberplates is a thin layer of epoxy into which are embedded a layer of glass beads which are specified as being around 75?m in diameter. These are supplied in powder form and it's easy to produce a diffuser by applying a thin layer of epoxy and then dipping the item in the powder or brushing the powder on the item - when driven with light from behind the layer the light remains quite bright but very even.

Bottom line - I'm going to have to fiddle about aren't I

[Mike E (uk)]

Another advantage of switching the illumination off with the lights is that the dash bulbs last a great deal longer. Or perhaps you were changing those to LEDs too?


Mike

[electrokid]

I had a couple of dash bulbs fail a few years ago and replaced the whole lot - not had any problems since, so while it would be nice to change to LEDs it's not a problem so it's not going to be fixed.

When I bought the car I noticed that the clock would only display if I was hammering round a left hand corner and hit a bump at the same time. I wrongly assumed that the feed to the clock was intermittant - it was over a year before I investigated and got it working by the simple expedient of replacing the bulb Now that it has failed again I'm thinking that there are a couple of things that could cause that !

First there could be additional or different vibration in that area of the dash, and second, even when turned up full, the dash bulbs are fed via the brightness control pot so have a small amount of resistance which may help them survive better whereas the clock bulb does not.

So I'm going to leave the dash bulbs alone - but along with your idea of controlling the clock brightness along with the dash brightness I'll try to be aware of the possibilities - there could be a number of possibilities. There are LED replacements already available for the dash but the control AFAIK is less effective - because the LEDs take less current. So any mod to the clock could be paired with normal dash bulbs and its control, or LED dash bulbs and any modified control for those - we shall see.

[mat_fenwick]

A couple of things to help diffuse the LED if too direct:
Roughen up the domed tip with a bit of wire wool - easy to do and may be sufficient for your needs. Obviously the less pointy the tip, the wider the viewing angle so if you actually reshape it that should help more. Or cutting off the dome, and drilling a depression in the surface should work - I've seen what I term an inverted cone LED shape on Christmas lights and this seems to scatter the output pretty well.

I have to say I've not had to change the clock bulb in over 120k miles in the same BX, so wonder if there's something else amiss?

EDIT - that could be as I rarely travel with no lights on, so the clock is usually dimmed...

[electrokid]

I'm familiar with the roughening and cutting off the dome but drilling out I've not heard of - but actually that should do the trick and would be neater than the solutions I had in mind - I'll give it a whizz

[mat_fenwick]

Like this:



You can try it on what arrives in the post tomorrow

[electrokid]

That has all arrived Mat - thanks - much appreciated

I've sorted out which pins do what and since they are standard 4mm spades I should be able to knock up a jig no probs. The PCB, the LCD and the tiger tail were cleaned with IPA and then reassembled and the clock is working ok. Removing the lampholder PCB there's enough room to poke a 10mm LED through the hole.

I played around with a 10mm LED without much success - I'm guessing that the filter is also a diffuser (hence Vanny's orange carrier bag being successful).

I did have a look at some Christmas light LEDs this afternoon as I happened to be in Woking (which is quite rare these days !) and I wasn't impressed - the 'drilled out' section simply produced a shadow straight ahead with a bright halo around - but then the one in your picture has a much greater angle - greater than a normal drill for example, whereas the one I saw this afternoon had an angle which was less than a normal drill bit would make. I'm figuring the 'drillbit' angle needs to be around 90 degrees so it effectively forms a circular mirror with all surfaces at 45 degrees.

When I replaced the bulb last time I bought 2 bulbs - with absolutely no illusions that I might be able to find the second bulb again when I needed it and sure enough I can't find it yet.

I will find or buy the right bulb though - then I'll check the light output (I have many meters including a luxmeter) and try to replicate that with an LED. One reason that the quick tests didn't look hopeful was that I tried it plain and then I tried it drilled - and it was a 10mm LED with 140,000 mcd output... but then I was only running it at 10mA and without a diffuser.

I'll have another play when I get more time.

Edit - 'all surfaces', not 'ball surfaces'

[Vanny]

The PCB, the LCD and the tiger tail were cleaned with IPA

Was the IPA from Green King or another brand?