This started as an EPICS 3.15.5 plus synApps 5.8 IOC (xxx-5-8-3 template) to watch various sensors using the GPIO capabilities of the Raspberry Pi.
| sensor | description | support | comments |
|---|---|---|---|
| ADS1115 | 4 Channel 16 Bit I2C ADC | planned, use I2C bus | see data table |
| DHT11 | humidity & temperature | superceded by DHT22 | too unresponsive |
| DHT22 | humidity & temperature | complete (v1.0 release) | reads every 1s |
| LDR | light-dependent resistor | planned, use ADC over I2C | voltage divider circuit |
| HC-SR04 | ultrasonic range | planned | |
| HC-SR501 | PIR infrared proximity | planned | |
| MCP4725 | 12 Bit 2.7V-5.5V I2C DAC | planned, use I2C bus | |
| NTC10k | thermistor (temperature) | planned, use ADC over I2C | voltage divider circuit |
Already, we have integrated many of these sensors on Arduino connected by USB to the RPi and integrated in EPICS using the cmd_response protocol. This project eliminates the need for the Arduino. Deployment is simplified on the very small form factor Raspberry Pi Zero W, which needs only a power source and access to WiFi in order to become an EPICS IOC on the LAN.
Once built, the SD card can be imaged to create many such Raspberry Pi sensor
IOCs, each having an identical array of sensors.
The only customization needed for each RPi is to set its unique hostname.
My practice is to base this name on the last four text characters in the output of
/proc/cpuinfo (part of the unique RPi serial number).
The IOC is configured to use this as its PV prefix, ensuring (with some confidence)
that all its PVs will unique on the subnet. Such as:
pi@rpi170f:~ $ cat /proc/cpuinfo | tail -1
Serial : 000000004887170f
pi@rpi170f:~ $ sudo hostname rpi170f
Then, all PVs will start with rpi170f:, such as:
| EPICS PV | meaning |
|---|---|
rpi1705:pin0:humidity |
most recent humidity reading |
rpi1705:pin0:temperature |
most recent temperature reading |
It is possible but not likely to have two RPIs on your subnet that match. If you are so unlucky, add another digit or two to avoid this.