Isothermal

isothermal

An Arduino shield which regulates temperature. Originally, this was used to regulate the temperature of a Hammond 1590BB.

• schematic
• gerber files
• OSHPark link
• EEVBlog discussion

The resistor values were chosen to map a 20C to 30C window onto (roughly) 0V to 3.3V.

See also this link for PID tuning and measurements of a similar design (based on MCP9701 rather than thermistors).

Bill of Materials (BOM)

FIXME: update this BOM for v1.2.

• (1) LM324 op amp, DIP14.
  • Tayda.
• (1) 2N3904 TO-92 NPN transistor.
  • Almost any TO-92 transistor should work here.
  • Tayda.
  • The footprint is for a TO-220, in case you need to use a bigger transistor.
• (2) 10k thermistors.
  • I use Vishay NTCLG100E2103JB which are about $1 each from Digi-key.
  • You could also get away with cheap epoxy bead thermistors, though if the Beta is different you'll need to calibrate the gain of your controller.
• 1/4W resistors, 1% metal film (precision-ish):
  • (2) 10k.
  • (4) 33k.
  • (2) 120k.
  • Tayda.
• 1/4W resistors (non-precision):
  • (1) 100R
  • (1) 470R
    • The LED resistor -- 330R or 220R will also work.
  • (1) 1k
  • (4) 100k
  • Tayda.
• (9) 0.1uF ceramic capacitors, through-hole or 0805.
  • Tayda.
• (1) 10uF electrolytic capacitor, 25V, 5mm diameter, 0.1" (2.5mm) lead spacing.
  • Tayda.
• (1) 3mm LED.
  • Tayda.
• (4) 2-pole terminal block, linkable, 0.2" lead spacing.
  • Digi-key.
  • Note: don't get the cheap (ebay) ones with the phillips-head screws -- the screws are garbage and the heads will strip. If you go cheap, get the flat-head screws. I ordered these and they seem to do the job: https://www.ebay.com/itm/182525842695
  • I'm not sure the Tayda parts will work, as they are 5mm spacing, rather than 5.08mm, which might be a problem when you link 4 of them together and expect them to fit into 0.2" holes.
• 0.1" male headers: a block of 10, 8, 8, and 6.
  • These are the Arduino pins.
  • Actually, you only need 10 pins: 3.3V, 5V, GND, GND, A0, A1, AREF, AREF's GND, D3, D2.

If you are using this to heat a Hammon 1590BB, you'll also need:

• (1) Hammond 1590BB Aluminum enclosure.
  • Tayda.
• 1/2W or 1W (heater) resistors.
  • (10) 10R
    • Tayda.
• Some thermal epoxy. Arctic Silver is easy to source. Walmart has it for $6 at the moment.
• (2) "craft foam" (9x12 sheets, 6mm)
  • Amazon.
• Hot glue to secure the foam to the Hammond case.
• Very thin gauge wire to connect the remote thermistor. Scrap Ethernet twisted pairs will work (26 AWG), but 30 AWG "Kynar" (wire-wrap) wire is better (less error due to heat transfer along the wire). Thin-gauge "magnet" wire will also work.
• An Arduino.