Thread: High Bright LCD

okay that's simple.
Since the controller dishes out 0-5V, I just tested the resistance of pin6 at the inverter. Put one lead to the pin and another to the inverter's ground--I got 445K ohms. If we put a 500K resistor between the controller and the inverter, it will be a series drop. Half the voltage will drop over the first resistor, bringing it down to 2.5V. I guess the best way to see if it works is to test the voltages at the nodes forward and behind the resistor.

Originally posted by SinnerG
ddogg_777
Where did you measure the resistance from? Obviously one end is at the output pin on the controller, but where did you find the 'other end?" Although 500K wouldn't surprise me because usually you'd want a high impedence from the output to allow the load (inverter) to get most of the current.
As for the OSD, I never really messed with it, but maybe it does have brightness controls. Another thing to check while I wait for relief.

Okay, I see an error in your thinking. The brightness control voltage is a reference voltage, not a supply voltage. Very little, if any, current passes through this line. The inverter has a circuit inside it that I call a reference transistor (for lack of the proper term) that merely reads the voltage that the controller sends to it. But in order for there to be a voltage to read, the circuit must go to ground (it's a law) because voltage is a potential. Since the R.T. circuit does not draw current, a resistor must be placed in parallel with it so that it has a voltage to read. The manufacturer chose a high value (500K ohms) so that a minute amount of electricity is dissipated.
Now back to what I stated before. If we put a 500K resistor in series with the circuit, the voltage has two dropping points. The max voltage of 5V will drop 2.5V after the first resistor (the one we put in) and then the R.T. circuit will read this new voltage before it is passed down over another 500K resistor to ground...
capiish!?

I've got the bulk of what you're saying, except is R.T. supposed to mean R total (total resistance)?

My take on your technique is:
If you measure resistance from pin 6 to ground, you're measuring the total resistance of the entire circuit, including the IC's as well as various other components that are in the 'path' to ground, but may not necessarily have an impact on the reference voltage needed to adjust brightness.

Also, you mentioned before about the problem with your powersupply not outputting enough current. try it again, but check the voltage. I remember using a PS that gave 12V, but when connected to my setup, dropped to 9V. This happens because the current is maxed out to its potential, but voltage has to compensate.
E=IR
since R is constant, the circuit will drain the current needed to work, but will drop the voltage. This is all based on a inferior PS. If you have one that offers more current, there will be no problems.

Yeah, Allen - get more of those controllers

Seriously, though - are there any chances of Datalux closeing out on the old controllers and going to the next rev?

- Jeff

Edit: Look at the way I spelled 'closing' - Hah!

Sorry, R.T. is my "reference transistor". You are right, there might be other resistances before and after the R.T. circuit makes its read of the voltage, that's why I said the only way to be sure is to test the voltage at the nodes in front and behind the 500K resistor that I will insert. And yes, my crappy Radio Shack Power Supply sucks! It can only dish out 12 watts and I now the lcd controller takes half of that. Today or tomorrow I will get some wire and hook up the inverter's voltage supply to my ATX supply (yellow wires are 12V, right?!)