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As many of you may know. If you have the Megasound9x board, that you lose the EL backlight facility that was offered with the early Smartieparts programming board. Not being one to rip out the EL backlight, it was time to modify things to make the backlight work.

First thing to do, is to take out the Smartieparts board and remove or isolate the Pogo pin that connects to PB7 on the main board, that happens to be the pin that is connected to 'VDD' on the Smartieparts board.

Now to the Megasound9x changes. The changes need to be made to the area around T2 as shown in the schematic below. The cut is marked in green. Added link in red. R5 to be removed. Board rear in original state. Track between R3 and T2 Cut. R5 Removed Link fitted between R3 and to what was the output from R5 Wire added to Smartieparts 'VDD' which goes to '-BL' of the Megasound9x That's all that there is to it. You can do this other ways of course. This is just one of them. :

Hi to all,

I have done it but it doesn't work to me.
From Spartieparts board need anything else to do except to remove the pogo VDD and connect VDD with -BL to megasound9x ?

That is all that is required to be done on the hardware side. Recheck that you have cut the track from the R3 (10K resistor) and the base of T2.

Is the same mod necessary with smartieparts rev 2.3 board?

Just to note, that I have the v2.3 and i did not need to use it for BL as i connected directly to MegaSound9x

I have a question on electronics...
Why do we keep R3 (10K) in the circuit between Megasound's Atmega and VDD pin on Smartieparts?
I thought 150 Ohms would be a better fit...

The way I did the modification was more about the ease of doing it physically rather than anything electronic. Personally I prefer using the 10K in series with the Atmega and the VDD in case something silly happens.

The current levels involved in using a 10K (that is already there) is very low and the voltage drop across the 10K is minimal and will have no effect on the operation of the system. Using the 150 Ohm resistor doesn't gain you anything. Of course if you wish to use that instead of the 10K resistor, you can as it will work just as well.

Ah, ok. I thought maybe there's some special reason behind that value, so I had to ask...

It's clear now.
Thanks a lot!

Hugh... At first, I used 150 Ohms resistor, and the BL stayed permanently ON. It got dim, sometimes flashed, but didn't switch off completely. So I changed the resistor to 10K and all became good.

But then I noticed another issue: whenever my radio is 'talking', the backlight switches off, and then resumes as soon as audio playback finishes. Strange... Looks like Atmega on the MegaSound board doesn't give sufficient power to VDD on the Smartieparts...

Perhaps, the 10K resistor is too much in my case... Hmm...

Mmm... I just swapped the 10K resistor with a 3K9. Same thing...
When BL is ON, the VDD is ~3.3V. When an audio file is played back, the VDD drops to just under 1.5V. When the radio is not in use and BL is off, the VDD still stays at around 1.5V.
Is this an expected behavior?

My solution to the backlight problem
A toggle switch I can turn it on and off Why do things the hard way?

A toggle switch I can turn it on and off

I made the same thing when I just got the BL (btw, I installed the switch to the power supply connector hole - it fits quite nicely there!).
But then I realized that switching it on and off automatically (by firmware) is so much more convenient!
After all, there is such a feature, it is convenient and it works great - why not to use it?!

My particular issue is related to the voice board. It may be just my board (which is a little strange, as schematic of that part is literally straight forward), or maybe a feature that I do not understand, yet. That's why I'm asking...

andrewju wrote:But then I noticed another issue: whenever my radio is 'talking', the backlight switches off, and then resumes as soon as audio playback finishes. Strange... Looks like Atmega on the MegaSound board doesn't give sufficient power to VDD on the Smartieparts... Perhaps, the 10K resistor is too much in my case... Hmm...

Just checked my transmitter and it works as it should. The backlight stays on when a voice file is being played. back. This is with the modification done as per the first post.

andrewju wrote:When BL is ON, the VDD is ~3.3V. When an audio file is played back, the VDD drops to just under 1.5V. When the radio is not in use and BL is off, the VDD still stays at around 1.5V. Is this an expected behavior?

I wouldn't expect the VDD to change at all when an audio file is being played back. It sounds like the current draw may be too high when a file is being played back, that is shutting down the regulator or you may have a high resistance path in the supply to the Megasound board. If you turn the volume level down, does the backlight work as it should?

Flaps 30 wrote:Just checked my transmitter and it works as it should. The backlight stays on when a voice file is being played.

Thanks a lot!

Flaps 30 wrote:I wouldn't expect the VDD to change at all when an audio file is being played back. It sounds like the current draw may be too high when a file is being played back, that is shutting down the regulator or you may have a high resistance path in the supply to the Megasound board. If you turn the volume level down, does the backlight work as it should?

No. It still goes off when a file is played.

I checked another board (outside of the radio). When the BL is OFF, the voltage on the leg of Atmega328 responsible for BL control is 0. On the board installed to my radio it is always around 1.5V, and raising to 3.3V when the BL is turned ON.

I tend to think it is another faulty Atmega, although it is very strange: I already changed the Atmega on this board because the first one didn't go past bootloader. Hmmm...

Hmm... Replacing Atmega helped! Now the BL works correctly even with a 150 Ohms resistor (actually, it should work without a resistor at all, but that's a bit dangerous in case if the wire going to BL gets shorted to ground).

It is the THIRD Atmega I have to put on this board...
Hope it will work fine now!

Reading the SD card may be the problem some of the cheaper cards may draw to much current while reading or writing.
It may be worth trying another card to see if that helps.

After all, there is such a feature, it is convenient and it works great - why not to use it?!

Because I've got a much more advanced computer attached to the toggle switch that can make a fuzzy logic decision on the light levels!

Bill wrote:Reading the SD card may be the problem some of the cheaper cards may draw to much current while reading or writing.
It may be worth trying another card to see if that helps.

This is probably a good point. But the old Atmega provided 1.5V when the BL was supposed to be OFF (even without SD card plugged in), so there was definitely something wrong with it. The new Atmega works with the same SD card just fine.

Bill wrote:Because I've got a much more advanced computer attached to the toggle switch that can make a fuzzy logic decision on the light levels!

I don't trust mine much: it always tends to appear multitasking, and get busy with many other tasks while forgetting about the things it's supposed to keep under control. So I prefer such mission-critical items as BL control to be governed by a simple and tested solution.

Maybe one day we will have the possibility to use RGB backlight, who knows?

Sent from my GT-I9195 using Tapatalk

A holographic projection would be even more interesting!

Yeah, right between our eyes and the model.

Sent from my GT-I9195 using Tapatalk

Yeah, right between our eyes and the model.