Dimming Instrument illumination

[wiltsathome]

Has anyone with a late model Caterham with LED illuminated instruments found a way of dimming them using a PWM rheostat or potentiometer? 
I find the brightness of the instruments blinding at night and would prefer to dim them rather than simply putting an on/off switch into the circuit
Look forward to your possible solutions

[Jonathan Kay]

With LEDs the most common current (!) fix is sticking a sticker in the way. Some people use a bit of sticky tape but you can buy purpose-built stickers!

Recent discussion.

Jonathan

(David White's solution)

[Roger Ford]

Is the problem with the instrument illumination in general, or the brightness of warning lights (most obviously the high beam light)?

And if it's the general illumination, do the instruments only light up when the vehicle lights are on, or are they always illuminated?

If they're only on with the lights, then it would seem worth experimenting with a PWM on the lighting-circuit feed to the instruments. Whether it would work on not would depend on whether the LEDs are fed directly (or through a simple voltage reducer), or whether they have on-board drivers.

If it's the high beam, that's going to be fed from the general power circuit, so I can't see anything being possible without dismantling the whole instrument.

[Jonathan Kay]

"Is the problem with the instrument illumination in general, or the brightness of warning lights (most obviously the high beam light)?"

Ah... I assumed it was the warning lights. Good question.

Jonathan

[wiltsathome]

Cheers guys, the problem is the white light background lighting to the instruments that on my 2016 car are like Blackpool, dazzling forward vision and reflecting so badly in the side screens that the mirrors are useless. Happily, my high beam light isn't too bad (better than my previous 2006 car)

The easy solution is to put a switch into the red/white feed off the back of the light switch, the snag with this is that you cut all illumination to both instruments and the switch indicators. Next option is to take each feed to each instrument into one switch and leave the switch illumination intact. But the ideal fix is to find a way of dimming the lights to switches and instruments with something like an old fashioned rheostat but I know some LEDs won't work with a normal voltage reducing rheostat.  
I'm therefore looking to see if anyone has found a good way of achieving the latter solution 

 

[Jonathan Kay]

I've got the factory wiring diagram if anyone would like a copy.

Jonathan

[wiltsathome]

That would be most handy Jonathan, if it for a 420r would it be possible to email on wiltsathome@hotmail.com please?

[Jonathan Kay]

Wilco

Jonathan

[Roger Ford]

I'm therefore looking to see if anyone has found a good way of achieving the latter solution 

I think you might be blazing the trail here. First thing I'd try would be to add something like this into the lighting circuit 12v-24v mini dimmer controller, but I strongly suspect that will just reduce the voltage. Might work, very unlikely (IMO) to damage anything and it's dirt cheap (not sure about postage). If not, you'll need to go PWM. There are loads of DIY PWM dimmer circuits on the web, but few ready-built ones. It looks like this PWM motor controller might do the job, even though it's designed for something completely different.

Of course for this to work, you're going to need to isolate the lighting feed to instruments and switches, you don't want to be PWM-dimming your headlights or tail lights.

Look like an interesting winter project, but my 2014 310R doesn't suffer from the same issue - otherwise I'd give it a try.

[Roger Ford]

Just one more comment, often reducing the voltage to LEDs will have no effect until you reach a certain level, then it will start dropping. So, for example, if you have 3.5v LEDs and a 12v feed, the driver circuit will reduce the supply voltage to 3.5v for output, and won't care if you give it 15v or 8v. However once you get below, say, 5v, it won't be able to sustain the 3.5v output and the output will drop. That assumes the driver is using a constant voltage output, if it's constant current it probably wouldn't work the same way.

I don't suppose you have a bench power supply? If you did you could remove one of the instruments and see the effect of reducing voltage from 12v down to, say, 1.5v and see if the instruments eventually dim, or whether the lighting just suddenly switches off at a certain level.

[wiltsathome]

After a little surfing I have found a purpose made Stack dimmer that appears to be suitable and is packaged for instillation, a little dearer than stuff on line but those options are not so well packaged for easy car installation. factor in the club discount and we will see  will report back after I have tried it

https://www.demon-tweeks.com/uk/search/shop-by/q/Stack%20dimmer/

[SM25T]

As owner of a 2002 car, we can only dream of being able to illuminate instruments to that level !!

[SLR No.77]

https://www.demon-tweeks.com/uk/stack-led-dimmer-switch-for-stack-gauges-stast269114/

I have Stack versions for both my oil and coolant gauges and they're very bright, actually really nice quality gauges. I'm tempted to fit one of these to reduce the brightness a little though!

Stu.

[wiltsathome]

The Stack dimmer works well on the standard instruments from full bright to fully off. What is really useful is that the red needles are the last to go out as you decrease the light so you still see where the needles are without the background. An ideal mod for safer night driving
I tried to post a video but this site rejects the format. 

[Jonathan Kay]

Thanks for the update.

...

The site can show videos inline but TTBOMK no-one knows how to upload them.

How about Dropbox or YouTube?

Jonathan

[Colin Heseltine]

Wilt,

Can you tell us how/where you connected this into the instrument light feed.  Cable colours etc.

Where have you located the dimmer controll.

Thanks,

Colin

 

[wiltsathome]

The instruments lights are fed by red and white wires into the bottom right of the wire block as looking from the instrument face. I took the feed to the dimmer from the wire into the RevC and Speedo, then picked up each instrument feed from the dimmer output. I located the dimmer under the dash on the top side of the panel that has a grommet in it for accessing the diagnostic plug, simply drilled a hole for the dimmer spindle to poke thru so it is above you right knee and easily found pretty much directly below the main  switch. 
happy to chat directly if you want more details. 
cheers

[Jonathan Kay]

Thanks for the details.

Can I help with serving the video... and did you sketch the new wiring layout?

Happy Christmas

Jonathan

[Colin Heseltine]

Wilt,

Sorry for slow response but many thanks for those details.  As Jonathon says a sketch of the wiring and maybe a photo of the dimmer in place would be useful.

Colin

[wiltsathome]

 

Apologies, I haven't been on the forum recently. However, a few photos are attached​  

The first photo shows the dimmer switch knob under the dash and easily found whilst driving and strapped in. I may put a rubber or plastic knob on it to make it easier with gloves but as I rarely wear them I probably won't get around to it. The dimmer switch sits on the top side of the aluminium plate that is under the dash and contains the large rubber grommet that gives access to the diagnostic / management plug. It's not visible as it hides behind the radius of the bottom edge of the dash

second photo shows normal full illumination and the reflection in the side screen, whilst the third shows the lighting dimmed to such that the digits renaming readable and there is effectively no reflections in the side screens. The last photo shows them dimmed such that just the needles show. They can of course be dimmed to no light at all

as for wiring, it's simple. Cut the red and white feed wire into the tacho and Speedo and from the loom end connect them together along with the feed into the dimmer. I do this with solder and heat shrink, tidy and way more reliable than connectors. Pick the earth up on the side of the main light switch and solder the dimmer earth onto the small spade end that connects it. Then cut the feed into the other three instruments, seal the loom ends with a double layer of heat shrink to terminat and then bridge the feed wire from the dimmer into each of the instrument plugs. If I could have got a wiring diagram and find the feed at the fuse or relay box I'd have done it that way, but I couldn't find the wire without major dismantling that didn't warrant the effort in my view. 
 

hope this helps 
 

[Jonathan Kay]

Thanks for the details and the photos.

Jonathan

[StevehS3]

Looks great and thanks for writing it up. My new (to me) car appears to have incandescent bulbs but I think it may suffer from the over-bright blue main beam LED. If it does I will add a resistor into its feed.