ESP8266 Community Forum

- Tue Jan 09, 2018 12:12 am #72988

Based on the schematics I posted in my previous reply, I imagine that T1 on the Sunbeam power schematic is an Isolation Transformer (ie. the 7V circuit is induced by the 240V with no direct connection, and then rectified by the diode bridge)?

Yes.

Whereas the Breville seems to just regulate down the Line Voltage?

That machine is using what is called a "capacitive power supply". It's not isolated from mains and while the voltage between the output pins is only 24V, each pin has up to ~325V relative to mains earth (assuming 230V RMS mains voltage).
So as btidey already said: don't touch anything while the machine is connected to mains and don't hook anything up that referenced to mains earth (like an USB cable to your computer or an oscilloscope).

The use of an LM7805 in the sunbeam makes me hopeful it should be sufficient to power my ESP8266 circuit as well as the factory IC.

That depends on the transformer and what else is hooked up to the 5V rail, but you have a much better chance than with the Breville.

Capacitive power supplies only provide very low current (for higher currents, you'll need huge caps) and to make matters worse for you, the Breville just uses a resistor and zener diode instead of a proper voltage regulator. I don't think you can reliably power an ESP with that design, unless you use a separate power supply.

Even though the Sunbeam's schematic is very incomplete, it seems to be a much more sophisticated design.
It's using triacs instead of relays for the heaters/motors and seems to have a zero cross detection, which suggests it can chop the A/C waveform and therefor has a much finer control that just on/off.

- Tue Jan 09, 2018 7:29 am #73001 Sunbeam certainly seems to be better engineered so if it is better machine that makes it a good choice.

As previously mentioned the T1 transformer powering the electronics makes it isolated and much nicer and they use opto isolators to trigger the triacs which are on the live side so that is good.

For powering the 3.3V line for the ESP8266 I would actually start from the unregulated DC voltage across C1. This is probably around 9V dc. Doing it this way avoids loading the 7805 further and any worries about whether it could then get too hot. I would then use a simple buck converter e.g. mini MP2307 on ebay to regulate that down to 3.3V. These are very cheap and efficient so there is little extra heat even when regulating down from 9V. I would also replace C1 with a higher value (say 1000uF) as the 100uF is small and there will be a lot of ripple. I suspect the current electronics are fairly low power so they used a lower value for C1 but with ESP in there you want a steady voltage.

By all means use level shifters for monitoring the signals into the esp but you can use fairly high resistors in a potential divide to avoid any disturbance (e.g. 68K/100K).

For control I would still just put either bjts or mosfets in parallel with the switches you want to control. Either would do the job; the bjts would need say a 10K resistor in series with GPIO pin to the base, emitter to ground, collector to the hot side of the switch. GPIO low means the bjt or mosfet is off and GPIO high closes the switch.

Last edited by btidey on Tue Jan 09, 2018 7:50 am, edited 1 time in total.

- Tue Jan 09, 2018 7:46 am #73002 It looks like the flow meter is wired into the interrupt line on the processor so I suspect that is counting pulses to ascertain flow. One could certainly monitor that line in the esp8266 but it would need some experimentation to translate pulses into flow.

U2 HT24C02 is a small serial EEPROM probably being used to store some settings; maybe a timer schedule?

- Wed Jan 10, 2018 4:03 pm #73052 Thanks so much Btidey & Lethe! That's a huge help for me. It looks like the PCB is quite cramped, and I want to replace the LEDs up by the switches on the front panel anyway, so I may look in to cramming the ESP up there too, away from the hydraulic components. Really excited to have a crack at this. Thanks again.