**Automating a dumb kitchen hood with Home Assistant**
Last month I had to repair my kitchen hood – replace its PCB – and I got an idea how to automate it.
The idea is to turn it on automagically when something is cooking and the kitchen air gets stale. I already have a VOC sensor in the kitchen (Ikea Vindsyrka – see the blog post).
The hood was sold under the brand Respekta – which has same PCB as Baumatic an probably some other brands.
What else I need?
- something that presses the button on the hood instead of me.
Should I use fingerbot? Seems too clunky and limits the access to buttons. No.
Hardware
I figured out I need a ‘dry relay’ to make contact on the hood’s button. The device that only closes and opens the button’s circuit (without any voltage). I found 2 (zigbee):
- Aqara Dual channel T1 (~35€) and
- ZG-001(link to review on Smarthomescene), ~9€.
Firstly I thought I could use one of the spare Sonoff ZBminis I already had at hand, but they do not have a dry contact. There are some instructions on YT how to cut some contacts on its board, but I didn’t want to bother and ordered zg-001 switch.
The hood’s fan and light buttons are connected to the hood’s PCB via 5-wire cable. The port on the board is CN5:
After inspecting PCB from the bottom side, I saw that wires 1, 3, 4, 5 are connected to a chip and 2 to some resistor. So I thought that 2 must be GND and the others are control wires. I short circuited combinations of pin 2 and others and the fan turned on. Short circuiting wires 2 and 1 turns on the fan on the lowest speed – exactly what I need. I removed a bit of insulation on these two wires and soldered an extension wires:
Reconnected the connector to the PCB:
I also added one 230V cable for powering the dry relay switch. I put both cables through the hood’s ventilation holes. I could install the dry relay switch within the cover, but I wasn’t sure the zigbee signal will penetrate through it. So I decided I will mount it on the outside of the hood’s cover.
This hood’s covers are quite tricky to dismount and remount, I needed 2 people to help me.
Now I’m waiting for the dry contact relay to arrive.
Dry contact switch
The switch arrived and I mounted it on the outside of the hood. Connected 230V for power supply and wires for the parallel connection to the hood fan button/contact. This smart switch can also be powered with USB. Other models also with variable DC power sources (7-32V).
Home Assistant / zigbee2mqtt recognized it immediately after powering it on.
It shows up as Tuya ZG-001:
Home Assistant automation
Now, the automation.
Firstly, I need to simulate short hood button press. I achieved that with a simple automation that turns off smart switch 200ms after it detects it has been turned on:
Next, I want the hood turns on when the air in the kitchen is dirty (something is cooking).
I already have Ikea Vindstyrka (see the post) sensor nearby.
The automation turns on the hood for 2 minutes when it detects VOC is above 230 for 1 minute:
It’s very simple automation, but it works. It doesn’t matter if I cook something, baking in the oven or nearby toaster – it turns on because of increased VOC. That is good.
Some ideas for the future
The issue is that VOC is dropping slowly over time, even with hood turned on. I don’t want the hood runs for extended periods of time, because it is quite loud.
I have to figure out how how to solve this issue. One idea is to install another, IR sensor under the hood and capture HOB2HOOD signals from the hob and turn the hood off when the hob isn’t active. Will see how the current solution will work out.
Also, I’m not sure if VOC 230 is a good threshold. Maybe it would be better if I set-up thermostat like entity in Home Assistant so I (or other family members) can increase or decrease VOC threshold without changing the automation. Not sure how to implement this, because the hob switch reacts on a press, not on a on-off state.
https://blog.rozman.info/automating-a-dumb-kitchen-hood-with-home-assistant/
