Ondio Backlight Mod
(preliminary article, to be completed)
Let There Be Light!
The Ondio is internally prepared for an EL display backlight, but on the units we've seen this is not equipped. We don't know why, either it was creating interference, or hard to get, or Archos just saved on the components. The strange thing is that Archos even changed the driver chip when Sipex moved out of the EL market, so they actively maintained the feature. The Archos software is driving the backlight port pin, Rockbox had to learn it.
Personally, I miss the backlight and decided to mod my unit by equipping the missing parts. Making a more simple LED backlight was no real option, there is not enough space behind the display.
EL stands for electroluminescence. The effect is that certain phosphors are glowing when exposed to an alternating electric field. An EL foil contains such a substance between 2 electrodes. It takes a high AC voltage to excite it, but little current. Typically, about 200V with 200 Hz. A specialized inverter chip (with a coil) is used to generate such from standard DC supply.
The good thing about EL lighting is the completely even lighting of the area, and that the foil can be cut into almost arbitrary shape, as long as you don't cut away the connector electrodes. The downside (compared to LED lighting) is a certain wear of the phosphor, it is not suitable for continuous operation. The brightness is noticeably going down in the range of 1000 hours. But for our backlight this should be sufficient. The power consumption is comparable to LEDs.
The closest match to the size we need I could find is here:
There is also a link to a small swedish web shop where it can be ordered. It comes with a little inverter assembly, but unfortunately not the chip we need. However, the simple way would be to just wire it somehow, there is space e.g. between the main and the tuner board. I went for the more aesthetic solution, wanted the original assembly. However, I took the inductor and the capacitors from the kit, although no perfect match. For the required circuit, see the EL driver datasheets in the DataSheets
Still too big: original and trimmed foil, with the inverter from the kit:
Bill of material:
EL foil in suitable size
Sipex SP4403 or NPC SM8141BV?
, depending on your model, below for SM8141B?
470uH SMT inductor
100V SMT diode
100V 100nF SMT capacitor
200kOhm SMT resistor
10kOhm SMT resistor
10-100nF SMT capacitor
It requires SMT soldering equipment and skills, a very limiting factor, besides the required components.
The missing parts are back:
The look with the foil and LCD sandwich:
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