| ??? 04/24/05 10:25 Read: times |
#92257 - opto Responding to: ???'s previous message |
Don't get me wrong, it was just an idea, not a proven working circuit. The nonlinearity can be compensated by callibration to certain extent, or maybe by a choice of "nonlinear" resistors (there are also "linear" optos around, or "linearized" using a suitable feedback); but the temperature dependence of CTR would be probably a bigger problem. Anyhow, I would never attempt to use such scheme (even without the decoupling) to detect simultaneously pressed keys; and then it is enough to determine "thresold values" to discriminate between the keys - that's where the nonlinearity gets really out of question. An another idea, if you permit, is using a "keypress-dependent oscillator" (e.g. using a 555) and feed it hrough an opto into timer/counter input of the mcu. It is not necessary to push the use of one or more mcus in each and every gadget one builds... :-) Maybe another vague idea?: Try the old charging/discharging a capacitor through the resistors in series, the buttons shorting them out. Having two capacitors at each end, properly rated, you get decoupling without optos and with minimum number of parts... 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 |