Calibration

[jcozzarelli]

Is there any way to calibrate the temperature? It is almost 15 degrees too high.

[Tony]

If you have the early version using a 220 (22uH) coil change it for a 33uH, that will improve it considerably. If it is the new version check the soldering round the TCN75 sensor and that it responds to temperature changes, if it's not soldered correctly it'll use data from the less accurate DHT11 sensor. The TCN75 sensor used is accurate to +- 0.5 degrees and the output is digital so no calibration is required.

[Tony]

I've just noticed - 15 degrees not 5 - that would indicate a serious fault, either a faulty sensor or the board is drawing too much power and cooking. What was the current reading across R28 before it was fitted?.

[jcozzarelli]

Hi tony
I have the 22uh coil. Where do I get the 33?
I don't recall the current draw but it seemed reasonable. I will double check.
I will recheck my assembly
Joe

[jcozzarelli]

Tony
I had a long lead that was limiting the contact to the sil pad.
The temperature is much closer. I's say within 5 degrees.
Where can I get the alternate 33 uH inductor?
Not a radio shack item.
Joe

[Tony]

Most component suppliers such as Mouser or digikey can supply the inductor but that mod is only intended to reduce slight self-heating. Such a large error wouldn't be caused by that.

Is the board around the sensor IC getting warm and could you give an example of the display versus actal temperature?.

Edit - just refreshed and read your latest post.

This is the type of coil you need:

http://uk.farnell.com/multicomp/mcsch89 ... dp/1864377

There are a few on ebay from China but you'll probably have to buy 20 for $3 or so.

[jcozzarelli]

Hi Tony
I believe it is self heating.
When I first turn on the unit, it is very close to the accurate room temp. Within a degree or two.
After about 5 to 10 minutes it reads about 5 degrees warmer than it actually is.
I will try the 33uH change.
Joe

[jcozzarelli]

Tony:
Trying to get 1 inductor is extremely expensive. Most component suppliers have a minimum order quantity that makes it unreasonable.
After spending $180 for a kit, I think that it is reasonable for you to support your product and ship me the updates as required.

Joe

[Tony]

You should be able to find sellers on ebay offering packs of 10 for about $3-4 including post. Let me know how much and I'll refund the cost, which will still be half the postage from here and would be there faster.
The one you need will be described as '8x10mm 33uH'

[jcozzarelli]

Tony
This is what I ordered. Will it work?
Joe

Order placed
March 31, 2014
Order Details | Invoice
Order #114-9217835-5597846
Recipient Joe Cozzarelli
Total $12.60

MURATA POWER SOLUTIONS - 13R333C - STANDARD INDUCTOR, 33UH, 1.8A, 10%
Sold by Materro LLC