Thermostat (Olimex EVB)

Thermostat — Olimex ESP32-EVB

A wall thermostat on a 2.8" portrait screen, driving the two relays the board has. There is no temperature sensor on it: a simulated measurement sweeps the range, so the heating relay audibly clicks around the setpoint the moment you download it.

Project: examples\olimex_evb_example.yaml Board: Olimex ESP32-EVB with a MOD-LCD2.8RTP, 240×320 portrait Needs: nothing wired up — it runs in simulation as it is

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What it shows

A complete small project, of the kind most first projects turn out to be: ladder logic with hysteresis, a screen somebody can operate, a manual mode, a trend, alarms — and a WEBview page shaped for a phone rather than copied from the board.

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The screens

Home. The gauge is the measurement, the buttons below adjust the setpoint, and the switch turns automatic mode on and off. One screen that answers "what is it doing" and "make it do something else".

Manual. Every actuator on its own. This is what you want during commissioning, and what you want when something has stopped and you need to find out which part still works.

Note that manual heating only acts while automatic mode is off — the interlock is in the logic, not in the screen, so it holds however the value is written.

Trend. Two traces recorded in the board, so the history exists whether or not anybody is watching. The current values sit under the chart, where they can be read without interpreting the lines.

States and motion. Two lamps on one variable — one taking its colours from a named set, one with its own — a panel whose background is the state, and a marker that travels the scale as the setpoint moves.

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The logic

Five rungs, and the shape is worth reading:

1. A heartbeat — one BLINK on a spare output. The cheapest diagnostic there is: anybody at the board can see the program is running, without a laptop.
2. A simulated temperature — SEL, RAMP and PT1 producing something that behaves like a real measurement, so the thermostat has something to do on a bench.
3. The thermostat itself — a HYST comparator. Two parameters, and the entire control loop.
4. The relay — automatic AND cold, OR manual AND commanded.
5. The setpoint buttons — a rising edge into an addition, so holding the button does not run the setpoint away.

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Worth copying from it

• the hysteresis block driving a relay. The smallest complete control loop there is, and the answer to a surprising share of problems.
• a manual screen that mirrors the automatic one. Costs an afternoon, saves a day the first time something misbehaves.
• a heartbeat on a spare output. One block.
• a WEBview page designed for a phone, not a copy of the board's screen — a big number, the state, and the two controls that matter.

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Try changing

• the hysteresis gap (ON and OFF on the HYST block) — watch the relay's rhythm change in the trend
• the filter constant on PT1 — a bigger T makes the measurement smoother and later, which is the whole trade-off in one number
• add a second alarm at a lower limit and watch it appear in the alarm table by itself

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Showcase — STM32F746	the same runtime on other silicon
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