Digital Ballast Bypass Expirimenting

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Tonight I made some headway on bypassing newer digital ballasts that require a signal rather than a simple short.

I got out my cheap osciliscope and took some measurements. It was interesting to find that on the projector sends a signal to the ballast then it seems like it waits for a reply. There is only 1 optocoupler sending back to the projector so I assume that this is the needed signal. The other 2 optocouplers i'm assuming are for the lamp enable and the input signal.

This projector has 5 wires going to the ballast.
1 - Signal Back to Projector
2 - Ground
3 - +5v
4 - Square Wave
5 - Signal From Projector

I measured the out and in signals and took some snap shots. The signal going to the ballast starts at 5v and drops to around 3v. The signal returning from the ballast starts at 0V and goes to 5V. The signals appear to be the same pulse width just offset and inverted.

Low Power Mode
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Med Power Mode
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Full Power Mode
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The microcontroller used in the ballast is this 1 here
http://www.nxp.com/documents/data_sheet/P87LPC769.pdf

The signal input to the ballast goes into pin 11 which is a serial input

The signal from the ballast goes to pin 12 which is serial output

The square wave goes into pin 8 External Interupt.

This ballast design for sure uses some sort of serial communication. I am positive that this complicates the bypass process greatly. For now I will do some reading and see what I can come up with.
 
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Indeed looks like a serial comms. Assuming a standard 8-bit control or command word, the last shots looks like a 10101011 data word.
The forward direction would be the command, the return would be the actual setting, (which of course when all went well would be identical to the command).
Educated guessing.
You can easily figure out the data values for the other modes.

jd
 
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Can this communication be emulated or would a similar microcontroller with serial com be needed? Its a challenge now. I need to prove that we are smarter than the ballast...hahaha


I dont know much about serial communication. I am reading that a start bit is sent then the 8 bits then a stop bit or bits. This would explain the return signal waiting for the complete input signal.

Looking closer at the data sheet, I would say its a very accurate guess that the Serial Port is running in mode 0 with external timing.

My guesses for the other modes are
Low
10 00 01 00 00
Med
10 01 01 11 or 10 00 10 11
 
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Can this communication be emulated or would a similar microcontroller with serial com be needed? Its a challenge now. I need to prove that we are smarter than the ballast...hahaha


I dont know much about serial communication. I am reading that a start bit is sent then the 8 bits then a stop bit or bits. This would explain the return signal waiting for the complete input signal.

Looking closer at the data sheet, I would say its a very accurate guess that the Serial Port is running in mode 0 with external timing.

My guesses for the other modes are
Low
10 00 01 00 00
Med
10 01 01 11 or 10 00 10 11

You can hang your scope's 2nd probe on a clock signal so you see the bit transistions clearly. You value for low has a few bits too many ;)

It's simple to build your own controller and play with the values and resulting brightness etc, using for instance a PIC microcontroller. You don't need to worry about start-stop bits and the like, that's all low level stuff handled by the micro and the development system (which, for the PIC is free). BUT you need to be somewhat experienced in this.....

jd
 
The brightness is actually controlled by the remote and the software on the projector. The different signals are sent for each mode to the ballast. I am trying to eliminate the ballast completly and just feed the proper message back to the projector so it thinks the ballast is installed and the lamp is working.
 
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Heres a question....Would a PIC be able to accept the incomming serial message then send the correct message back to the projector main board allowing the ballast to be removed? I know it would take some programming just wondering if the device is capable

Of course it is. This is 2-fingers-in-your-nose stuff. ANY PIC even the $ 0.85 12-series in a DIL08 can do that. Take a look at the microchip site.

I'm not familiar with this projector stuff. How does this work? You send a 'light level' command to the projector, then what happens? How does the lamp and supply and ballast work together?

jd
 
The projector has a main controller board and the ballast for the lamp. The main board controls all functions of the projector. In most projectors the main board sends a signal to enable the ballast and power on. Then the ballast sends a signal back to the projector that the lamp is lit and working. Usually by pulling the lamp lit signal low (grounding) most projectors are happy and will stay running with no errors. This is not the case with newer projectors that use serial communication.

This Eiki projector essentially works the same as most but uses serial communication.

The brightness modes are selected with the remote. The main board then alters the signal going to the ballast and the ballast responds accordingly.

The main goal is to remove the ballast and have the projector run giving no errors thinking that the ballast is still installed and the lamp is functioning. This requires requires:
1 - Recieving the signal from the main board.
2 - Processing the signal
3 - Returning the correct signal

I will post some schematics with more detailed scope readings. All signals to and from the ballast are isolated with opto-couplers. I measured the signal at the TX and RX pins of the microchip. I will post some signals before and after the opto-couplers for comparison on both input and output

Also...Please note that I appreciate you accepting the challenge to understand this and try to help figure this out. It will help me and many others continue to modify newer projectors.
 
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The purpurse of removing the ballast is so I can retrofit an HID or LED lamp and keep using the projector insted of buying a lamp for ~$300. The projector will run just fine with it removed as long as the projector thinks it is still talking with the ballast. This also cuts way down on power consumption as the projector isnt burning 250W into the lamp
 
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The purpurse of removing the ballast is so I can retrofit an HID or LED lamp and keep using the projector insted of buying a lamp for ~$300. The projector will run just fine with it removed as long as the projector thinks it is still talking with the ballast. This also cuts way down on power consumption as the projector isnt burning 250W into the lamp

OK, so if I recall your scope pics, it seems that the ballast returns the exact same commanded data but inverted, is that correct? So then, is it an option to just connect whatever comes out of the command micro back into the ballast input? Just looping the serial link, inverted?

jd
 
Here is a signal from the tx and rx of the microprocessor. It looks to have alot of noise but this is the signal going to the opto-couplers

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Here is a picture of the ballast and input wires.
Wires are as follows:




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Here is a signal from the tx and rx of the microprocessor. It looks to have alot of noise but this is the signal going to the opto-couplers

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Here is a picture of the ballast and input wires.
Wires are as follows:
RED - Signal Back to Projector From Ballast
WHITE - Ground
BLUE - +5v
YELLOW - Square Wave CLOCK
BLACK - Signal From Projector To Ballast

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This is where I get confused.....
The bottom 2 optoisolaters are for input. The middle one being the clock signal and the lower one being the serial information to the ballast.

I was looking at the data sheet for the isolaters and tracing the circuits.
http://www.datasheetcatalog.org/datasheet/vishay/83666.pdf

The top pins get +5V from the blue wire
The signal lines go through 100 ohm resistors and to the bottom pins(Most likley current limiting)

The other side of the the lower optocouplers feed into the microprocessor on the rx and clock lines

On the return the microprocessor feeds ithe tx output into a transistor then to the optocoupler and back to the board

The signals I meaured from the pins of the micro processor are not at all what I expected. The signal looks really noisy

I am thinking maybe I could cut out the micro processor and just bridge the TX and RX traces but I'm not sure it would work
 
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I decided to desolder the ballast controller from the actual ballast. I got some high rez scans of both sides. Unfortunatley it is a 4 layer circuit board. I am going to try to trace the circuit paths and create a block diagram from input to output. This might take a few days to complete.

Front Side
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Back Side
5003.jpg
 
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I did some circuit tracing. This thing is pretty high tech for just a ballast. Theres a whole lot going on with this little pain in the butt.

Front
FRONT.jpg

Back
BACK.jpg


I am wondering if it woudl be easier to buy a programmer for the microchip and try to redo the internal program eliminating ballast functions.
 
Well I managed to get a copy of the "Holy Grail" for this projector....AKA the service manual. Its funny that you were talking about using a PIC to communicate with the ballast. This projector uses a PIC to control all ballast functions.

After studying the schematics and trouble shooting. I figured that the Lamp_Err signal coming out of the PIC was the place to start. This signal is around 70mV and jumps to 5V when a lamp error is detected. This signal is sent through a buffer IC then to the main processor.

http://www.fairchildsemi.com/ds/74/74LCX541.pdf

By cutting the trace from the pic to the buffer and connecting the buffer pin to the buffer ground the projector stays on....

SUCCESS!! So far anyways. I havent tested for more than 2 minutes. I dont know what repeated errors will do to the pic or any other part of the circuit.
 
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[snip]I am wondering if it woudl be easier to buy a programmer for the microchip and try to redo the internal program eliminating ballast functions.

Don't if your are new to ucontroller programming. UYou can do it but the need to learn a whole new trade costs you a lot of time.

Better to find someone who is good at it already.

And don't forget you need to figure out the whole control logic structure first!

jd
 
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Well I managed to get a copy of the "Holy Grail" for this projector....AKA the service manual. Its funny that you were talking about using a PIC to communicate with the ballast. This projector uses a PIC to control all ballast functions.

After studying the schematics and trouble shooting. I figured that the Lamp_Err signal coming out of the PIC was the place to start. This signal is around 70mV and jumps to 5V when a lamp error is detected. This signal is sent through a buffer IC then to the main processor.

http://www.fairchildsemi.com/ds/74/74LCX541.pdf

By cutting the trace from the pic to the buffer and connecting the buffer pin to the buffer ground the projector stays on....

SUCCESS!! So far anyways. I havent tested for more than 2 minutes. I dont know what repeated errors will do to the pic or any other part of the circuit.

Well that seems a good solution!

jd
 
I just wanted to mention, if you're not careful, with that much of the plate through hole stuck to the ballast pins and a four layer board you could easily wind up with some discrepancies between what you see in the drawing and what's actually wired on the main board..

Luckily the only connections made are on the bottom of the ballast board. That board is only 2 layer.

Oddly enough these ballasts do not have a set wattage rating. The wattage is variable down to 0% now if through the service menu if the power output is lowered down to say 15% would the ballast still function and would it power a 35w HID lamp and not explode?
 
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