Let's Design a PCB for a Battery Powered WiFi uController

Electronics
#1

I’m teaching a class occasionally using a Wemos D1 Mini - a $4.00 microcontroller based on the ESP-8266EX. I currently have one monitoring a friends hot water circulation and uploading the return temperature every 20 seconds to the free ThinkSpeak.com site.
https://thingspeak.com/apps/matlab_visualizations/178190

This one is powered by a wall wart but I would like to develop a PCB to run for several months on battery power. There are lots of articles for similar projects but I have not found one that I like. Uses could be to monitor temperature or other sensors/switches where power is not readily available. It could monitor movement of outside gates, hot water heater moisture or temperature drop or garage door position and garage light on. Alarm conditions could trigger an audible alarm, light, email or tweet.

I strongly favor the Wemos board because it is cheap, very adequate and I have a bunch that I use for classes. I’m very flexible on other parts. I would like a simple one sided board which could be easily DIY fabricated without many physical wires. Is this feasible?

A simple MCU like the ATtiny85 could be the front end that uses 0.5uA during sleep and wakes up when a time expires or an input pin changes. This is much lower power than the 8266. I like the ATtiny85 chip because it can be programmed using an Arduino board. Development using a DigiSpark ATtiny85 w/ USB connector is handy but power usage is high due to other parts on the board like the LED. Final product would need to be the ATtiny85 chip to turn on an N-channel FET like an 2N7000 to wake up the Wemos.

The ATtiny at 1MHz seem to be tolerant of a wide range of voltages. Not so much for the 8266 which requires more power during transmit. I’m not familiar with buck/boost but could use some suggestions if that would be appropriate here.

When the Wemos receives power, it could set a pin high, read the sensor and transmit info as needed. The ATtiny could watch this pin. When transmission is complete, the Wemos drops power to the pin and the ATtiny drops power to the FET and go back into sleep mode. The Wemos would use no power while the ATtiny is sleeping.

Anyone interested in helping? In case this goes beyond a board that I could reasonably fabricate, what are your suggestions on having boards fabricated. How much would it likely cost to have twenty boards made.

#2

I am willing to help. I do not have the electronics background needed.

1 Like
#3

I recommend oshpark.com for several reasons.

  1. Predictable and reliable service
  2. US based
  3. Very high quality boards
  4. Easy with either KICAD or EAGLE, no gerbers to mess with.

It is not the cheapest, but then if I can avoid Chinese slave labor I do so. The other advantage, if your working on what you want to be a commercial product, you reduce the likelihood of that chinese cheap pcb manufacturer turning around and selling a clone of your product for much less then you can afford to.

BTW, getting several months on battery is going to be a challenge. Low power is an area that has many hidden skills. @zmetzing may be able to offer some guidance.

1 Like
#4

@Diplomat - I see you are in my Blynk class. I look forward to meeting you. My progress on this project will be covered.

@wandrson - Totally agree with your challenge point. That’s part of why I posted this - to try to line up all the help I can get.