Advice for reliability of heat thermostat

Projects General Guidance
1

Hello,

I'm doing a simple wireless thermostat for my house heating. I'm using those cheap nrf24l01 modules and arduino pro mini 3.3V 8MHz.
So I have two arduinos, one is powered with batteries, with a nokia 5110 display, a temperature sensor and a clock. If temperature drops from the setpoint, it sends a message asking to switch on the heater (or switch off in case of rising above setpoint). So nothing special or complicated.

But I ask you for advice because I'm afraid with reliability. I mean, The sender sends and order that usually is received and processed, but what about the order not being received?
So, as I'm using ack payloads there are different scenarios:
1- sender ----> receiver (message OK)
receiver ---_> sender (ack OK)

Everything OK, so no problem here,

2- - sender ----> receiver (message OK)
receiver ---_> sender (ack not received)

The heater switched but controller don't know.

3- - sender ----> receiver (message not received)
receiver ---_> sender (----- N/A ----)

in cases 2 and 3, I think I could keep sending until I receive the ack, but: how many times? kind of while (!ack)? or is better repeat just a number of times?

the real problem here is that the heater could stay in on state, heating too much. or stay off aloing the house to cool down too much.

So, any tip?

Thanks a lot in advance.

2

You need (kind of) a watchdog, to monitor a connection from both ends of the chain. The heater controller has to check the connection as well. As long as it receives commands every now and then, everything looks fine. If no message is received within some time interval, it should send a message to the master controller, and check whether the master sends back ACK, and/or the currently intended temperature. If not ACKed, enter a safe emergency state.

The definition of "safe" is up to you. In winter time the heater should still be turned on, if the temperature tends to fall below some "safe" value (8°C?).

3

Thank you Dr.
I will definitively follow your ideas.
Something has also brought into my mind, I could place a temperature sensor inside the receptor (which is connected to the heater) so your safe emergency state could imply checking its own temperature sensor. This could allow stopping the heating if temperature in the heater room increase above and hard-coded setpoint.

Thanks again.