Our hotel terrace has four patio heaters on cheap 433 MHz remote sockets. Staff forget to switch them on in the evening and forget to switch them off at night. I have a Raspberry Pi already doing the terrace temperature for Hermetry.
I read about the “Pi as an FM/RF transmitter with just a wire on GPIO4” hack and got excited, then confused. How does that even work, can a GPIO pin really transmit radio? Could I use that to send the socket codes? And then I’d like Hermetry to do it automatically: on at sunset, off at 23:00. Is that a rule or a flow?
The GPIO4 trick uses the Pi’s clock generator: it can put out a square wave at tens of MHz, and the software wiggles the frequency to make FM. A square wave is full of harmonics, so you’re also transmitting on frequencies you have no right to use. Fine for a lab demo, I wouldn’t put it on a hotel terrace.
For the sockets, a 2 dollar FS1000A 433 MHz transmitter module plus the rpi-rf Python package. Sniff the remote’s codes with the matching receiver first (rpi-rf_receive), then replay them.
ok I ordered the transmitter + receiver pair. So the Pi part is clear, but how do I trigger it from Hermetry at sunset?
Rules card. I run lab ventilation schedules this way.
First give the Pi’s profile a command, e.g. heaters.set with a Yes/no param on, Basic tier. On the Pi:
from rpi_rf import RFDevice
tx = RFDevice(17); tx.enable_tx()
CODES = {True: [5592405, 5592407, 5592411, 5592413],
False: [5592404, 5592406, 5592410, 5592412]}
def on_rpc(req_id, body):
if body.get("method") == "heaters.set":
for code in CODES[bool(body["params"]["on"])]:
tx.tx_code(code, 1, 350) # protocol 1, pulse length from the sniff
client.publish(f"v1/rpc/res/{req_id}", '{"ok": true}', qos=1)(Your codes and pulse length come from the sniff, mine are placeholders.)
Then on the terrace asset’s Rules card:
- Rule “Heaters on”: When Sunrise or sunset, Sunset, offset -15. Then Send a command
heaters.seton = yes to the Pi. - Rule “Heaters off”: When A time of day 23:00, every day. Then the same with on = no.
Sunset needs the place’s location, so put latitude/longitude on the terrace asset and place the Pi under it, otherwise the rule won’t save. Also, 433 MHz has no feedback, so send the command twice a minute apart if you want to be sure. Doc: Time, sunrise/sunset, dates and holidays.
Running for a week now! “Sunrise and sunset need this place’s location” was exactly the message I got, added the coordinates and it saved. I also added a second off rule at 23:05 because one socket misses the code now and then. Staff noticed nothing except the heaters are just on when they should be.
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