Hi, I recently built a Weather-Station using an RPi and Lazarus/FPC, but: anything that's not I2C or SPI (or otherwise supported within the RPi hardware) is IHMO hard to realize. I went on and used an AVR (Arduino) to interface the DHT11, and hooked that up to the Pi with UART (just before dumping it completely, because it's accuracy and self-heating issues were just to much to calibrate accurately).
Reason: Am 23.08.2018 um 11:11 schrieb Bo Berglund: > An alternate way would be to do an accurate sleep for a time between > the two limits, say 48 us, after seeing the pulse rise and then > determine the state of the I/O at that time. > If the input is 0 then the bit is zero and if it is still 1 the bit is > a 1... There are commands like usleep() in Linux. But - as the typical system on the Pi is not a realtime OS and we have the granularity of the system scheduler, task switching, interrupts etc. pp. to account for, many sources give it's accuracy to be only above 100 µs. Generally I would say that, on any complex system, without considerably effort, no loop or timer can be 100% sure not to be interrupted while processing input data for at least a few µs, which is exactly the problem here. One solution might be possible, though I never digged in further (and I suspect it's not possible for a user-land process, but I might be proven wrong): try do define your own interrupt on the specific pin (there are some libs for this, also in user-land) and find a hardware timer in the Broadcom chip that is running stable enough to count a few µs. There are timers and interrupts in the Chip (see https://www.studica.com/blog/raspberry-pi-timer-embedded-environments). Regards, Alex PS: I dumped the DHT11 and used a HTDU21D. I2C, stable and easy with FPC ;-)) _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
