Differenze
Queste sono le differenze tra la revisione selezionata e la versione attuale della pagina.
| Prossima revisione | Revisione precedente | ||
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notes:hd44780-vs-st7066 [19/11/2018 19:03] alez created |
notes:hd44780-vs-st7066 [19/11/2018 19:25] alez [The Hack] |
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| Linea 36: | Linea 36: | ||
| -2.0 to -1.1 is a good contrast and -1.5 can be considered a good average. | -2.0 to -1.1 is a good contrast and -1.5 can be considered a good average. | ||
| - | ===== Hack howto ===== | + | ===== The Hack ===== |
| I have encountered (in an UniOp EK42) an interesting contrast control circuitry, fortunately designed to comprehend wide range for Vo supply. It was enough to replace a couple of resistors to change the mathematical function and adapt the circuit from HD44780 to ST7066. | I have encountered (in an UniOp EK42) an interesting contrast control circuitry, fortunately designed to comprehend wide range for Vo supply. It was enough to replace a couple of resistors to change the mathematical function and adapt the circuit from HD44780 to ST7066. | ||
| - | {{:notes:alim-lcd.png?300|}} | + | {{:notes:alim-lcd.png?500|}} |
| With Vr that is a square wave from an MCU, with period about 10us, variable duty cycle; Vcc=5V, Vee=-5V (about). | With Vr that is a square wave from an MCU, with period about 10us, variable duty cycle; Vcc=5V, Vee=-5V (about). | ||
| Linea 52: | Linea 52: | ||
| | R6 | 18k | 130k | | | R6 | 18k | 130k | | ||
| - | Original values meant a V0 from about -0.18 to +1.2 V (duty 50% gives about +0.5V) | + | Maths: |
| + | |||
| + | V0 = R4/R3 * R2/R1 * Vr - R4/R3 * (R2+R1)/R1 * R6/(R5+R6) * Vcc | ||
| + | |||
| + | Note that Vee is not critical. | ||
| + | |||
| + | Original values meant a V0 from about -0.027 to +1.35 V (duty 50% gives about +0.65V) | ||
| Modified values mean a V0 from about -2.5 to -0.5 V (duty 50% gives about -1.1V) | Modified values mean a V0 from about -2.5 to -0.5 V (duty 50% gives about -1.1V) | ||
