Category Archives: MOSFET

ESP8266 Progress

There can be no doubt that I still have some way to go in terms of reliability with my test rig in Spain before putting this stuff in charge of the heating back home in the UK:

  • Raspberry Pi 2 is on an un-interruptible supply but does not 100% recover from loss of broadband. One example made my Apache instance disappear until I rebooted the Pi !! I’ve just instigated a check for Google connectivity every 15 minutes leading to a reboot if no success – hoping this will solve the problem.
  • ESP8266 board mostly recovers from power failure but I have one example of it simply not communicating until next power cycle. Will soon do some tests removing the power for various periods from milliseconds upwards.

Highcharts - click to enlargeOther than these points, I’m starting to get somewhere.  I have plant-watering control running, a kitchen light under dusk to midnight control using my Node-Red scheduler referred to elsewhere – and as of this morning I’m logging external temperatures locally every 15 minutes using MQTT and Node-Red to ask for temperature, MQTT, Node-Red and MYSQL to store the temperature (as read by a DS18B20 using my own ESP8266 fast code) and local HighCharts and PHP to read the temperature from the DB (including missing values) on a chart on the Pi (up to now I’ve always used GroveStreams for everything but I’d like to try storing information locally). I’ve documented all of this in previous blog entries. At some point I want to scrap the PHP and use JS within Node-Red.

Scheduler - click on the image for larger versionBuilding up to this seems such overkill – but then now it is done, the sky is the limit – setting these up (below – and remember – click on any image to show full size version) took no time at all. I used the scheduler with a new addition to my little ESP board, a timer option which turns the output (ESP-01 for example) on on request for X minutes – the board then turns the output off all on it’s own.

So for the watering I just sent the same message at dusk and dawn, a timed request for 4 minutes of watering. I figured dusk and dawn were as good a time as any and no chance of blasting hot water onto the plants (believe me, in Spain if you try this at lunchtime from a typical black pipe watering system, you’ll fry the plants).Node-Red

The lower block above simply puts out the temperature request every 15 minutes and above that an MQTT block picks up the incoming temperature and fires in insert command off to the MQTT node.

Si2302Meanwhile I’ve been pondering a device I’d not specifically come across until yesterday, the Si2302 N-channel MOSFET.  From EBay these work out at a few pence each (like, 3p in quantity) and are simply tiny SMT devices (but large enough to solder by hand).  I’m thinking these might do for powering LED strips, both simply on-off control and PWM.  If I’m reading the spec right, these should work just fine from the 3v + output of an ESP8266 with no other components (no base resistor for example) and with 1 amp’s worth of LED STRIP (12v) attached I reckon the chip should dissipate no more than 80mw. Of course my maths could be miles out but I’ve a few samples on the way to give this a shot and if they pan out I’ll stick them on the next board.

Has anyone had any experience of this particular MOSFET?

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