Hello
I am an embedded software engineer and can cope with things digital, but struggle a bit when it comes to analogue and transistor biasing - especially where negative voltages are involved.
I am using a graphics STN LCD panel and want to control the contrast. The panel has a negative voltage generator output (Vout) and a contrast control pin (Vo). The datasheet says just put a pot between the two. However, I want to be able to control contrast from software, and digital pots won't work outside of their supply range. I have a DAC output from my processor that I can control between 0 and 3.3V, but how do I use this to control the contrast voltage I need? I'd be grateful if someone could suggest a circuit to do this. I'm sure it's just a transistor and a few resistors!
From the data sheet...
http://docs-europe.electrocomponents.com/webdocs/06dd/0900766b806dda11.pdf
Vdd-Vo is 16V. I will be using Vdd of 3.3V. It doesn't say what Vout is, but I guess it's a few volts more negative than -16V.
Thanks for any help.
I am an embedded software engineer and can cope with things digital, but struggle a bit when it comes to analogue and transistor biasing - especially where negative voltages are involved.
I am using a graphics STN LCD panel and want to control the contrast. The panel has a negative voltage generator output (Vout) and a contrast control pin (Vo). The datasheet says just put a pot between the two. However, I want to be able to control contrast from software, and digital pots won't work outside of their supply range. I have a DAC output from my processor that I can control between 0 and 3.3V, but how do I use this to control the contrast voltage I need? I'd be grateful if someone could suggest a circuit to do this. I'm sure it's just a transistor and a few resistors!
From the data sheet...
http://docs-europe.electrocomponents.com/webdocs/06dd/0900766b806dda11.pdf
Vdd-Vo is 16V. I will be using Vdd of 3.3V. It doesn't say what Vout is, but I guess it's a few volts more negative than -16V.
Thanks for any help.
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