Talk:Freezer to Refrigerator Conversion

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Revision as of 02:37, 23 October 2018 by Dorkmo (talk | contribs) (→‎To Do)
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math

What temperature should a refrigerator be?

The FDA recommends between 32°F and 40°F (0°C to 4°C).

Energy Star recommends between 35°F and 38°F (2°C to 3°C) to reduce energy use.


thermister =

10K Ohm @ 25 celcius
20.13 @ 5
24.30 @ 0

voltage devider

Vout = (R2/(R1+R2)) x Vin

24.3 Ohm -> 0.962V
24 Ohm -> 0.97V
21 Ohm -> 1.06V

Analog to Digital Converter

Arduino's onboard ADC converts voltage to a range of 0-1023 based on arduino's base voltage

so on a 3.3V arduino, analogRead(A1) will equal

0V = 0 reading
1.65 = 511
3.3V = 1023

so

24.3 Ohm = 298.25 = 0 C
24 Ohm = 300.88
21 Ohm = 329.99

Relay Trigger Voltage

Arduino MKR 1000 is a 3V board. The Solid State Relay minimun trigger voltage is 3V. I had trouble getting the relay to activate. measured 2.8V. This was not enough to trigger. I changed the wiring to share a ground with the temperature. May need a diode? Sparkfun makes a 5V board. going to switch to that, but need to figure out where im losing the 0.2V.

  • try using the 3V out pin then pull to ground?

MKR1000

could use VCC pin on MKR1000 to connect to the Relay (+) terminal, then pull to ground the relay's (-)

"VCC This pin outputs 3.3V through the on-board voltage regulator. This voltage is the same regardless the power source used (USB, Vin and Battery)." - https://store.arduino.cc/usa/arduino-mkr1000

Buttons-arduino.png

Potentiometers to dial in HI and LO temp

To Do

  • might try using Digital out pins to send voltage to Pots
    • might need a plain resistor between the digital out and pot
      • calculate for max 30mA at either 3.3 or 5v
  • Set 50% point on both knobs as 36 fahrenheit
    • Max knob turn adds 5, Min turn subtracts 5.

or could have pot#1 set the mid point and pot#2 change the allowed range

Other Aplications

Air Conditioner

  • with a WiFi enabled microcontroller, could possibly remote control/monitor an air conditioner window unit. Could also schedule run times.
    • would need to make sure air conditioner start up routine doesnt require button press.
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