Talk:Freezer to Refrigerator Conversion: Difference between revisions

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thermister =  
==thermistor ==


:10K Ohm @ 25 celcius
:10K Ohm @ 25 celsius
:20.13 @ 5
:20.13 @ 5 C
:24.30 @ 0
:24.30 @ 0 C


==voltage devider==
==voltage divider==


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


:24.3 Ohm -> 0.962V
:24.3 Ohm -> 0.962V = 0 C
:24 Ohm -> 0.97V
:24 Ohm -> 0.97V => (24.3-24)/(24.3 - 20.13) * 5 = 0.4 C assuming linear resistance of thermistor
:21 Ohm -> 1.06V
:21 Ohm -> 1.06V => (24.3-21)/(24.3 - 20.13) * t = 4 C


==Analog to Digital Converter==
==Analog to Digital Converter==
Line 35: Line 35:


:24.3 Ohm = 298.25 = 0 C
:24.3 Ohm = 298.25 = 0 C
:24 Ohm = 300.88
:24 Ohm = 300.88 = 0.4 C
:21 Ohm = 329.99
:21 Ohm = 329.99 = 4 C


= Relay Trigger Voltage =
= Relay Trigger Voltage =

Revision as of 20:03, 17 January 2019

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.


thermistor

10K Ohm @ 25 celsius
20.13 @ 5 C
24.30 @ 0 C

voltage divider

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

24.3 Ohm -> 0.962V = 0 C
24 Ohm -> 0.97V => (24.3-24)/(24.3 - 20.13) * 5 = 0.4 C assuming linear resistance of thermistor
21 Ohm -> 1.06V => (24.3-21)/(24.3 - 20.13) * t = 4 C

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 = 0.4 C
21 Ohm = 329.99 = 4 C

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.

Links

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