| ??? 04/23/05 06:32 Read: times |
#92217 - go analog Responding to: ???'s previous message |
Don't try to replace the switches by (common) optocouplers. Rather, use the optocoupler in a way it really works - as a current-to-current device. Arrange the buttons and a single optocoupler's LED so that different current flows through the LED on pressing the buttons. Then pick up the voltage on the phototransistor's bias resistor (proportional to current flowing through the transistor), maybe buffering it on an opamp. Nonlinearity of current transfer is not of much importance here, but CTR changes over temperature (and from opto to opto) is - you need some means of initial setup and/or (re)callibration. But what is the point of having optocouplers, if the supply to the buttons (drived from Vref as you described it) is not decoupled? Jan Waclawek |
| Topic | Author | Date |
| ADC as digital input | 01/01/70 00:00 | |
| Saturation | 01/01/70 00:00 | |
| good point | 01/01/70 00:00 | |
| URL | 01/01/70 00:00 | |
| all good, but | 01/01/70 00:00 | |
| optocouplers | 01/01/70 00:00 | |
| Re: ADC as digital input | 01/01/70 00:00 | |
| go analog | 01/01/70 00:00 | |
| schematic | 01/01/70 00:00 | |
| It is possible to do but why..... | 01/01/70 00:00 | |
| opto | 01/01/70 00:00 | |
| Possible but troublesome... | 01/01/70 00:00 | |
| very informative | 01/01/70 00:00 | |
overcomming opto difference | 01/01/70 00:00 |