Making backlights for non-backlight gear

gmeredith · March 10, 2009, 01:43:52 AM

Has anyone tried putting a backlight into their Alesis SR16 or Boss DR660? These machines are a PITA to use in low light conditions. I'm thinking of taking the screen off my DR660 and drilling holes in the mounting PCB and installing LED's to shine through them through the LCD screen in some way. Someone also asked me about this regarding their SR16.

Has anyone experimented with this sort of thing?

Cheers, graham

Circuitbenders · March 10, 2009, 02:29:43 AM

Quote from: gmeredith on March 10, 2009, 01:43:52 AM
Someone also asked me about this regarding their SR16.

It wasn't a guy called Bert from germany was it?

I've been working on this on and off on the SR16 for a while. You can't light these screens from behind unless you peel of the silver backing foil and i've found it impossibly difficult to light them from the side even using the smallest ultra-bright surface mount LED's.
I suppose you could peel off the silver foil and stick some kind of diffusion sheet behind the screen but getting any LED's far enough away from the screen to actually get any light diffusion would be tricky.

The best way i came up with doing it is to either use two small cathode tubes mounted above and below the screen like we do on our TR707 mods, or even better to peel off the silver backing foil and stick a bit of EL sheet behind it. The major problem with either of these methods is power. The backlight inverter for either cathode tubes or a bit of EL sheet needs 12V DC and a whole lot of milliamps. Annoyingly the SR16 runs on 9V AC so short of adding another power socket for the backlight or completely rebuilding the power supply i'm not entirely sure how to go about doing this. Another problem is that the interiior of the SR16 has no RF shielding and is very prone to picking up noise, so it'd probably pick up no end of crap from the invertor.

Presumably the regulators in the SR16 could cope with feeding it 12V AC and it wouldn't be that hard to take a separate feed from the power socket and rectify it for use as DC power for the backlight invertor. I'm just wondering if anyone has any better idea of how to go about this.

Gordonjcp · March 10, 2009, 09:45:54 AM

Quote from: Circuitbenders on March 10, 2009, 02:29:43 AM
The backlight inverter for either cathode tubes or a bit of EL sheet needs 12V DC and a whole lot of milliamps. Annoyingly the SR16 runs on 9V AC so short of adding another power socket for the backlight or completely rebuilding the power supply i'm not entirely sure how to go about doing this. Another problem is that the interiior of the SR16 has no RF shielding and is very prone to picking up noise, so it'd probably pick up no end of crap from the invertor.

Presumably the regulators in the SR16 could cope with feeding it 12V AC and it wouldn't be that hard to take a separate feed from the power socket and rectify it for use as DC power for the backlight invertor. I'm just wondering if anyone has any better idea of how to go about this.

Do you remember I said a while back it's worth learning at least a bit of theory? The analogue bits in the HR-16 (and I don't see how the SR-16 would be massively different) run off +/-12V, but the device is powered by a 9V AC adaptor. Where does the 12V come from? From 9*1.4142, which is how you work out peak voltage from RMS.

You could add your own bridge rectifier and and smoothing cap to power the EL panel, or use the existing +12 supply. You'd need to make sure it was very very well decoupled to stop it crowbarring inverter hash back into the analogue supplies. In either case you might very well need a bigger transformer - but you're not using the stock Alesis tranny anyway, are you?

Circuitbenders · March 10, 2009, 02:13:13 PM

Quote from: Gordonjcp on March 10, 2009, 09:45:54 AM
Do you remember I said a while back it's worth learning at least a bit of theory? The analogue bits in the HR-16 (and I don't see how the SR-16 would be massively different) run off +/-12V, but the device is powered by a 9V AC adaptor. Where does the 12V come from? From 9*1.4142, which is how you work out peak voltage from RMS.

yeah, i understand this. I've done some measurements on the SR16 power supply and i appear to be getting +12.5V / -14V on the two rectifier diodes. I was mainly wondering if the normal smoothing caps etc would be able to cope with a current draw about 10 times as big?

I'm not that keen on the idea of actually taking the voltage from the normal 9V AC and adding my own rectifier etc even though it seems like the better way to do it, mainly due to the complete lack of space in there. I'm suspecting i won'r be able to have the invertor inside the case anyway though due to space and noise problems so i might just build something into a small box mounted on the side.

(EDIT)

Come to think of it, it might be a whole lot easier to use an invertor box for a PC cold cathode case lamp which presumably has decoupling onboard anyway, and use the +12V supply on the SR16. It could easily be bolted to the side and i won't have to mess around adding rectifiers etc.

deathbender · March 10, 2009, 04:52:48 PM

A small hint in the right direction may be some of the backlight concerned posts in this forum:

http://www.8bitcollective.com/forums/viewforum.php?id=3

http://www.8bitcollective.com/forums/viewforum.php?id=31

They have several ways of modding Gameboys with backlight, with 1-4 Leds from the side, a Pro Kit offered by some guy and an EL-Foil type of backlighting...

Gordonjcp · March 10, 2009, 05:45:28 PM

Quote from: Circuitbenders on March 10, 2009, 02:13:13 PM

Come to think of it, it might be a whole lot easier to use an invertor box for a PC cold cathode case lamp which presumably has decoupling onboard anyway, and use the +12V supply on the SR16. It could easily be bolted to the side and i won't have to mess around adding rectifiers etc.

That sounds like the perfect way to do it, especially if you're adding a box for switches, sockets etc.

gmeredith · March 10, 2009, 10:43:38 PM

Hey, you guys, this has been a great response!

Crusty: No the guy was from the US.

It's great you have actually delved into this exact issue with the SR16. I don't feel so alone!
So, there is a silver foil on the back of the display. Have you peeled this off and experimented with it? Is it hard to peel off?

I got the guy to take some photos of the display board for me (it looks like it's mounted directly on the button board). I was thinking of removing the display and then actually cutting away a rectangle cutout a bit smaller than the screen in the board directly behind where the screen goes. It looks like there are only a couple of circuit tracks in this area (it's hard to know whats directly underneath the display though) and I was going to just reconnect these tracks with some wires going around the perimeter of the display. Then I could mount a diffuser plate (believe it or not a white piece of paper works well in the experiments I've done with other stuff!) across this cutout, and then mount some LED's on the other SR16 board facing up at the cutout. Powering the LED's would then be simple, too.

Would this sort of thing work? I thought you might have a better idea what's going on underneath the display and know whether it's feasable or not.

Cheers, graham

Circuitbenders · March 11, 2009, 01:22:46 AM

Theres a mother of a surface mount chip on the board right under the display on the SR16, way more circuit traces than you could reasonably move. The display is connected to the control board using those LCD zebra connectors which means once you've taken it off you have to get it back in exactly the right place or you get gibberish on the screen. Its not that hard though as the screen sits in a moulding on the inside of the front panel and the control board can only be screwed back in one position. When you remove the screen from the board be very very carefull to make sure the zebra connections come off with the screen as i doubt you'll get them in the right position again otherwise.

The silver foil is pretty easy to get off but you tend to be left with a sticky mess on the back of the screen and once its off theres no going back.

gmeredith · March 11, 2009, 03:41:00 AM

Hmmm..okay. I don't think I'll go through with the board cutting exercise then. Shame about that , I thought it woulld be simple.

Cheers, Graham

Gordonjcp · March 11, 2009, 09:40:08 AM

How big is the SR16 screen? About as big as a Gameboy screen? You used to get screen magnifiers with a little light in them for Gameboys, perhaps that would be worth considering...

computer at sea · March 11, 2009, 01:59:14 PM

The SR-16 screen is about the size of a slide for a microscope.

gmeredith · March 11, 2009, 10:28:59 PM

It's bigger than that - you must be thinking of the HR16. The SR16 is about twice that height.

Cheers, Graham

computer at sea · March 12, 2009, 07:08:47 PM

Right. The good Alesis drum machine.

LoFi-Ninja · March 28, 2009, 02:59:35 AM

Regular LCD:

Well if your gear sports a LCD like the one in the HR 16 it's an "16*2 HD44780 LCD"
So if there's no backlight in it, it must be pretty old, but your in luck. The 16*2 HD44780 LCD must be the cheapest and most easely optainable lcd.. Comes in like 100 different text/backlight colour combinations. So if you got one without backlight you can just buy a new one.. I don't think you can get them without anymore.. Or you could change the LCD to match some crazy paint job colour scheme to finish it off..

Graphical LCD:

If you got the foil reflecting thingie.. DON'T remove the foil ! Unless you have new stock of reflector foil and the other foil I forgot, it's not going to work, and it's going to look like shit no matter what..
But if you have new stock of the foils you can sandwich a thin piece of plexi glass, CD cover, whatever in between..
You need to scratch the plexi.. Then you add LED's.. The scratches will mike the light reflect.. Anyways there's tutorials on this just have a search..

Gordonjcp · March 28, 2009, 09:37:03 AM

Just as an aside, I replaced the incandescent lamp backlight in my Philips FM1100 70MHz transceiver with a green LED. The bulb has a clever little current limiter circuit to hold it at 40mA or so, but that's obviously too much for the LED. So I wired a couple of resistors in parallel to shunt the LED (not series, that wouldn't work here) and sanded up the LED envelope to make the light more diffuse. It pokes through a perspex sheet behind the LCD that also serves to light up the volume knob. Oddly enough, the buttons below the display and for the numeric pad have their own individual LED backlights, but they're all wired together.