Timeline for Low-cost phototransistor to MCU interface
Current License: CC BY-SA 3.0
3 events
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| Feb 3, 2014 at 13:30 | comment | added | Phil Frost | @realtime more gain helps because the range of input voltages that would result in an output voltage between GND and Vcc becomes smaller as gain increases. When you have "enough" gain, even thermal noise is enough to saturate the amplifier. It only increases your sensitivity if you make it amplify the difference about 0V. A common-emitter amplifier has a threshold of 0.7-ish volts. Design your phototransistor circuit so at the desired light threshold the output is about that. Or, design a different amplifier with a different threshold. There are many solutions, but all involve more gain. | |
| Feb 2, 2014 at 19:36 | comment | added | realtime | I don't see how additional gain will help. There will still be an illumination level where the voltage output is not within safe voltage ranges. Moreover, this would increase the sensitivity significantly, wasting an important degree of freedom. Using an analog input is an option for the STM32F0, but for the STM8 in question all analog inputs are already taken. | |
| Feb 2, 2014 at 13:05 | history | answered | Phil Frost | CC BY-SA 3.0 |