BL+ Enable B/L question

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bahstrike

New member
First- let me gripe about the datasheet for CFAG12864E-WGH-TN. The PDF's raw text is great, but the drawings are nearly useless- they are such low resolution that text is extremely difficult to read or in some cases not readable at all. I tried zooming in to no avail; the res is simply that bad. Is a better copy available??


Secondly (and more importantly) I have a simple question regarding the Pin 19 (BL+) of the CFAG12864E-WGH-TN module. To enable the backlight, do I simply tie this pin to VDD? On the datasheet in the 'Level' column for 19 BL+ and 20 BL- (which claims N/C) there is only a weird box, which I'm thinking might be a missing unicode character if this module is originally from China or something :D
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cosmicvoid

Master
Here's my guess: since pin 19 (BL+) is described as an "enable" ( for the on-board EL inverter), it would connect to either gnd or Vdd to turn the backlight on or off.

Maybe the drawings for one of the other 12864 models are better. What details in particular are you looking for?
 
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bahstrike

New member
cosmicvoid: Agreed- this is what I am thinking but I'm glad for the second opinion. As previously mentioned, the Level column in the datasheet says H/L (high/low) for other logic pins but the weird box exists for BL+/- pins so I was a little concerned maybe some crazy symbol was belonging there. I'll continue to design my circuit as-is :)

CF Support: Thank you for the raw CAD files- being vector graphics, the quality is above and beyond! I notice that the Typical Application Circuit drawing from datasheet Page 8 is not included in the CAD files. It is not a big deal- I am understanding now the required connections. The first purpose of my post was to discover BL+ usage.

Thank both of you for the assistance.


I am still wary of the BL+ pin. Because there exists both BL+ / BL- I am assuming these might be the power inputs for the two. BL- is no connect, but I am thinking it might just be tied to GND. If this is true, it means that it is likely unwise to try and source BL driver power from direct pin on a microcontroller. I still want the advice whether it is acceptable to use TTL input or if I should provide a higher current source to this pin. The application circuit drawing does not show BL+ or if it does I cannot read it.
 
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cosmicvoid

Master
bahstrike said:
I am still wary of the BL+ pin. Because there exists both BL+ / BL- I am assuming these might be the power inputs for the two. BL- is no connect, but I am thinking it might just be tied to GND. If this is true, it means that it is likely unwise to try and source BL driver power from direct pin on a microcontroller. I still want the advice whether it is acceptable to use TTL input or if I should provide a higher current source to this pin. The application circuit drawing does not show BL+ or if it does I cannot read it.
Click to expand...
Without knowing the part number of the inverter chip, the current requirement of the enable pin is unknown. I suspect it is logic level (low current), rather than power to the inverter circuit.

Maybe the CFA "factory" support can answer that.
 
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bahstrike

New member
cosmicvoid thank you for your response. I just ordered one unit today for experimentation and prototype. If CF can validate the pin requirements that will be great! I'll continue to work on other portions of my circuit design until it can be discovered.

One interesting note, however, is that the power consumption difference with EL off (10mA) and EL on (40mA) would imply the EL driver requires 30mA, which should still be within microcontroller source/sink limits. However, if treated falsely as a logic-level pin and a resistor is placed in series that could turn the tables for the worse :p If it is a power pin, I'd rather use a transistor gate to supply current.
 
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bahstrike

New member
I recieved this module today.

To answer my own question (and hopefully somebody else's, if they are interested in this device):

BL+ is a power supply pin, it cannot be thought purely logic (voltage-level). Connected to +5v it consumes ~10mA (10.33mA max from my personal test). Could be connected to an I/O pin, but without a resistor and only if comfortable with drawing this much current.


Being an electroluminescent sheet, the backlight is VERY consistent across the whole display- much moreso than LED or cold cathode tube.


I may comment further on the quality of the device once I have it hooked up to the rest of the circuitry and begin to see pixels start to appear--- unfortunately that is going to take weeks more considering I haven't ordered the parts for the controller board yet!! Now that I know BL+, I may be finally ready..

Very pleased with the width of the device. From PCB edge to PCB edge, 2.25" which can manage to squeeze into my application.

on attached picture, the CFAG unit is left-most bottom-most large item. since this, i connected a tranny gate to the BL+ pin which apparently is there to stay. WISH I HAD FOREKNOWLEDGE
 

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