HC-SR04 & RF Transmitter on SprinklerPi

[Anonymous]

Hi Ray et al,

Can anyone confirm if it is possible to connect an HC-SR04 (http://www.micropik.com/PDF/HCSR04.pdf) ultrasonic sensor to the 8-bit inputs, as explained in https://rayshobby.net/announcing-opensprinkler-pi-v1-2. With the sensor running at 5V, power may have to come from somewhere else, as those run on 3.3V.
My plan is to use the new http get feature to sense the water level on a water tank, from the OSPi.

Also, has anyone connected a RF Transmitter to the A3 8-bit I2C? I am not sure if this is where it should be connected, or if it is supported? This was mentioned in the new 2.1.7 Firmware Manual and blog post (https://opensprinkler.com/opensprinkler-firmware-2-1-1-new-feature-control-remote-power-sockets/) , but only refers to OS 2+, does not mention the 1.4+ OSPi.

Thanks,

Francois.

[Ray]

The HC-SR04 ultrasonic distance sensor is a digital sensor, not an analog sensor. You should not connect it to the analog pins. Instead, you need to allocate two free digital pins for it. Because the sensor output is 5V (its powered by 5V), you should connect a 1K resistor from its output to OSPi’s GPIO, to avoid potentially damaging RPi’s GPIO. Alternatively, there are newer versions of HC-SR04 — called HC-SR04+, that can be powered from 3.3V and hence outputs 3.3V too. If you use HC-SR04+, there is no need to use the series 1K resistor.

Note that OpenGarage (www.opengarage.io) is a standalone WiFi-enabled sensor that can be used to sense garage door status, but also used to sense water level — it has a built-in HC-SR04 sensor. You may want to consider using OpenGarage as a standalone sensor.

About the RF transmitter, again, it’s a digital component, and you should not connect it to the analog pins.

[Anonymous]

Hi,

I have a OSPi v1.4+ (for RPI B+) and think it is too old to do RF-Transmit.
Here is a pic:

Thanks for the HC-SR04+ tip.. Will look out for it.

Francois

[Author]

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