Valant Posted August 10, 2010 Report Share Posted August 10, 2010 So I happened to find a cheap DMF5005N recently. I spent a few days getting it to work and it looks great. Despite what the datasheet said (or so I think it says), this is a negative contrast voltage display. Datasheet Here Notice that in section 3.1 of the datasheet that the "Recommended LCD Driving Voltage" has no negative signs anywhere! So, I assumed it needed a positive voltage for contrast. My power supply disagreed. Lo and behold, with a negative voltage, the LCD works! What gives? Is there a surefire way to determine what an LCD needs? Furthermore, I am playing around with another LCD, the DMC-50448N. Another Datasheet This datasheet, again under section 3.1, shows positive values for the voltages. But now I'm skeptical. Perhaps this one requires a negative voltage as well? Quote Link to comment Share on other sites More sharing options...
Imp Posted August 10, 2010 Report Share Posted August 10, 2010 In both datasheets, there is a schematic under 4.2 which shows how to connect the driving voltage. It's quite hidden...I'd missed that one too.. The 2nd display needs positive voltage, as Vo is connected to a voltage dividing pot between Vdd(+) and ground. Quote Link to comment Share on other sites More sharing options...
julienvoirin Posted August 10, 2010 Report Share Posted August 10, 2010 (edited) 1st LCD, section 2.1 Vcc-Vee = 23 if Vcc = +5V then that means that Vee is negative (remember some maths) Vee sets the contrast Section 3.2 : typical LCD Driving voltage : Vcc-Vee = +13V I let you solve this very complicated equation at 3rd degree. Your contrast is driven by a negative voltage. provide a source of -18V, DC 2nd LCD use the circuitry of the core to control it. it is a classical CLCD (toshiba driver). just use a 20K trimmer for contrast instead of 10K Edited August 10, 2010 by julienvoirin Quote Link to comment Share on other sites More sharing options...
Valant Posted August 10, 2010 Author Report Share Posted August 10, 2010 In both datasheets, there is a schematic under 4.2 which shows how to connect the driving voltage. It's quite hidden...I'd missed that one too.. The 2nd display needs positive voltage, as Vo is connected to a voltage dividing pot between Vdd(+) and ground. Aha, I missed that too. Thank you! I will read datasheets more carefully. 1st LCD, section 2.1 Vcc-Vee = 23 if Vcc = +5V then that means that Vee is negative (remember some maths) Vee sets the contrast Section 3.2 : typical LCD Driving voltage : Vcc-Vee = +13V I let you solve this very complicated equation at 3rd degree. Your contrast is driven by a negative voltage. provide a source of -18V, DC 2nd LCD use the circuitry of the core to control it. it is a classical CLCD (toshiba driver). just use a 20K trimmer for contrast instead of 10K The maths - I recall! Vee = Vcc - 13 I read section 3.2 prior, but I misunderstood it as "Vcc-Vee", like it were some special symbol, but it really is a minus sign. Many thanks. This makes a lot more sense. Quote Link to comment Share on other sites More sharing options...
julienvoirin Posted August 10, 2010 Report Share Posted August 10, 2010 you are welcome :thumbsup: Quote Link to comment Share on other sites More sharing options...
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