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4-channel TC meter and datalogger project
napier
Top  #626 Print Post
Posted on 03/07/2011 7:14 AM
Hooray.

After re-doing how the numbers were being read, and reversing my thermocouple (yes, and ice-cube shouldn't make the temp increase...) I now have some very compelling readings.

AMB raw 498 ambC 31.000000 filtered 496
AMBIENT 31.000000 THERMO -332
CURRENT TEMP 22.801630 PID RESULTS 5153.886230

For calibration, what is the best known value to measure with the thermo? I suppose boiling water is predictable?
 
JimG
Top  #627 Print Post
Posted on 03/07/2011 9:18 AM

Quote

napier wrote:
For calibration, what is the best known value to measure with the thermo? I suppose boiling water is predictable?

Ideally, you would like to check/calibrate both the gain in the ADC, and the temperature offset in the MCP9800.

If you have an accurate millivolt source (like a thermocouple calibrator instrument), then you can use a 50mV signal to calibrate the gain in the ADC conversion. A small gain error, on the order of much less than 1%, may show up based on my experience with the TC4.

Once you have the gain calibrated, then you can successfully determine the temperature offset by comparing your results to a known reference point (distilled ice slurry is easiest, and very accurate at 32.00F).

The difficulty with checking the boiling point of water is that it varies with your altitude and the local barometer. But if you make the necessary adjustments to the theoretical BP value, then you could use a two point calibration (32.0 and BP) and calibrate both the ADC gain and the temperature offset.

Jim
 
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napier
Top  #628 Print Post
Posted on 03/08/2011 11:49 AM
Hrm,

How do I connect the small millivolt signal to the thermo? Can I just put a battery's anode to the tip and ground the cathode and get a signal? Is that too large a voltage to actually calibrate it? Because I can use a multimeter to verify the voltage to some degree if that's the case.

Otherwise I more or less out of kit.

Have you had to do much offsetting? I imagine it's dependent on the ambient measurement's proximity to the connector pins, the thermocouple itself, and how you're measuring with the thermocouple...
 
JimG
Top  #629 Print Post
Posted on 03/08/2011 5:54 PM

Quote

napier wrote:
Hrm,

How do I connect the small millivolt signal to the thermo? Can I just put a battery's anode to the tip and ground the cathode and get a signal? Is that too large a voltage to actually calibrate it? Because I can use a multimeter to verify the voltage to some degree if that's the case.

Otherwise I more or less out of kit.

Have you had to do much offsetting? I imagine it's dependent on the ambient measurement's proximity to the connector pins, the thermocouple itself, and how you're measuring with the thermocouple...


You would need a thermocouple calibrator, or similar instrument, as your millivolt source. Without that, your best bet would be to use the thermocouple itself for calibration (boiling water, ice bath).

I usually see somewhere around 1F to 2F offset error in the system when I run through a calibration. The gain error is normally very small. If you are using the TC4 as a roast monitor, you can easily get away with not doing any calibration.

Bill and I have been discussing a calibration software application for the TC4 that would require a type K thermocouple, some boiling water, and an ice bath. This is something I hope to have ready for use in a few weeks.

Jim
 
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bvwelch
Top  #630 Print Post
Posted on 03/08/2011 6:51 PM
I'm happy to help with this calibrating of the TC4, but it is the least of my worries -- I have way more errors and variability trying to figure out the best place to fasten the probes in the roasters. :-)
 
JimG
Top  #631 Print Post
Posted on 03/08/2011 10:55 PM
The TC4 version 4.00 PCB's have arrived and are available to order.

Price for the bare boards will still be $6 each, plus a couple of bucks for 1st class mailing. After PayPal fees, bubble mailers, etc. this should come out very close to break-even for me.

Because so many folks have requested it, I am going to also offer the TC4 boards with all of the surface mount devices (SMD) pre-soldered. (You will still have to solder the through-hole components). The SMD version of the board will cost you $16. This will cover the costs of components and solder paste, plus the bare PCB itself.

This page has links you can use to order the boards:
http://www.mlgp-l...o-pcb.html

On this page you will also see links to order the LCDapter board I've been using for an I2C interface to a 16x2 LCD. The bare PCB is available ($6). You can also order a bare PCB with the SMD's soldered on, plus a 12" cable to connect the LCDapter to the I2C header on the TC4 ($15).

Jim

PS -- the reset button is a very handy feature on the new V4.00 TC4 boards
 
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greencardigan
Top  #632 Print Post
Posted on 03/09/2011 12:21 AM
Payment made for 1 tc4 board with smd parts soldered. Delivery to a lazy guy in Aust.

Does the smd price include the EEPROM? The buy page doesn't mention if it's included.

Intend to give this a go with a PicAxe microcontroller rather than an Arduino.
Edited by greencardigan on 03/09/2011 12:25 AM
 
JimG
Top  #633 Print Post
Posted on 03/09/2011 10:55 AM

Quote

greencardigan wrote:
Does the smd price include the EEPROM? The buy page doesn't mention if it's included.

Yes, the EEPROM is included. Leaving that out of the description was a foobar :| Thanks for bringing it to my attention.

Jim

PS - got your order!
 
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mhoy
Top  #634 Print Post
Posted on 03/09/2011 11:52 AM
Jim: I figure I may as well have you do the surface mount soldering. :-) I'm in for the V1 LCD (that we PM'd about already), 2 of the TC-4 and 2 of the new LCD boards. I got my shipping info from SparkFun this morning too. Mouser/Digikey is next.

I should be able to be more involved soon.

Thanks
Mark
 
ginny
Top  #635 Print Post
Posted on 03/09/2011 1:06 PM
This is a test, would someone just reply to this post with anything?
gB)
 
t-rob
Top  #636 Print Post
Posted on 03/09/2011 1:32 PM
Just ordered the TC4 and an arduino uno. Very excited! Thanks to all for making this project possible.
 
mhoy
Top  #637 Print Post
Posted on 03/09/2011 2:24 PM

Quote

ginny wrote:
This is a test, would someone just reply to this post with anything?
gB)

anything.

Roflmao

Mark
 
aindfan
Top  #638 Print Post
Posted on 03/09/2011 9:22 PM
Jim, your new revision makes it very hard to order my own PCB... I still might though, given the number of SSR outputs I need. Can you clear something up about the LCD setup, though - do you use the basic LCD or the serial enabled LCD?

Thanks again for your hard work on this!
 
JimG
Top  #639 Print Post
Posted on 03/09/2011 9:49 PM
I'm using the TC4's I2C serial interface to talk to the LCD. This requires a port extender (the LCDapter uses the 16-bit MCP23017).

But in return for this minor inconvenience, you get to use a simple phone cord for your LCD cable, you get 4 buttons, you get 3 software-controllable LED indicators, and you do not use any AVR ports.

The LCDapter accepts any of the basic 16x2 LCD's that have a 16-pin header along the top left edge of the display.

Jim
Edited by JimG on 03/09/2011 9:51 PM
 
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mhoy
Top  #640 Print Post
Posted on 03/10/2011 11:07 AM
Anyone else having problems opening the v4BOM.pdf at:
http://tc4-shield.googlecode.com/svn/trunk/hardware/V400/

Mark
 
aindfan
Top  #641 Print Post
Posted on 03/10/2011 4:01 PM
Jim, thanks for your reply. I believe I read earlier in the thread that a 20x4 lcd will work as well (but physically will not fit on the LCDapter board) - can you confirm this? Can you explain the difference between the 6 LCD pins on the TC4 board and using the LCDapter (is this a matter of sending 4 pin I2C rather than 6 signal pins, power, and ground)?

(One thing that I just noticed on the TC4v4 schematic that clears things up: the LCD header output pins are wired directly to the Arduino DIO[2,4,7,8,12,13] pins, meaning that the LCDs are directly controllable by the Arduino and the LCDapter is there to compress the signal to I2C, send it a long distance, and decompress it at the other end.)

EDIT: My understanding is that a serial enabled LCD allows use of the Arduino TX pin connected to the LCD RX pin. Therefore, it should be possible to use a serial enabled LCD with the Arduino serial interface instead of the LCDapter and I2C with similar results, correct?

Thanks again!
Edited by aindfan on 03/10/2011 4:09 PM
 
JimG
Top  #642 Print Post
Posted on 03/10/2011 4:10 PM
A 20x4 LCD actually works just fine. The only issue is that it will cover up the spots on the LCDapter where the buttons and LED's get mounted.

Your options for using a 20x4 with the LCDapter would be:

1) live without the buttons and indicator LED's, or
2) mount the buttons and/or LED's elsewhere, and run jumper wires to them.

Jim
Edited by JimG on 03/10/2011 4:10 PM
 
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JimG
Top  #643 Print Post
Posted on 03/10/2011 4:15 PM

Quote

aindfan wrote:
EDIT: My understanding is that a serial enabled LCD allows use of the Arduino TX pin connected to the LCD RX pin. Therefore, it should be possible to use a serial enabled LCD with the Arduino serial interface instead of the LCDapter and I2C with similar results, correct?

I'll have to defer to someone else on this one. My immediate wonder, though, is whether or not the RX/TX pins are going to be busy talking to a PC, and therefore unable to deal with the LCD?

Jim
 
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JimG
Top  #644 Print Post
Posted on 03/10/2011 5:01 PM
I've just uploaded a few photos of the LCDdapter to the googlecode site.

Bare board:
http://tc4-shield...RE-800.jpg

SMD-populated board:
http://tc4-shield...MD-800.jpg

Arduino, TC4 shield, and LCD (connected by telephone cable). A white/blue 16x2 LCD display has been soldered to the LCDapter, and a simple button/LED testing sketch is running:
http://tc4-shield...61-800.jpg

Closeup view of the LCD display, the buttons on the LCDapter, and the LED's on the LCDapter:
http://tc4-shield...60-800.jpg

If you use the larger 20x4 LCD panel (which still works), then the buttons and the LED's will be covered by the display.

Jim
 
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bvwelch
Top  #645 Print Post
Posted on 03/10/2011 5:12 PM
I've been using one of Jim's LCDapter for about a week now, and I like it very much!

About the 'serial enabled' LCD -- don't bother with those -- just extra expense and probably a bit awkward to support. I suppose you could find a bit-banged serial I/O library and use some other I/O pins....

The beauty of going the I2C route is that you get the temperatures, buttons, leds, and LCD all daisy-chained on the same two pins.

If you need extra I/O for SSRs, why not just put them on a separate shield and stack on top?
Edited by bvwelch on 03/10/2011 5:13 PM
 
aindfan
Top  #646 Print Post
Posted on 03/10/2011 7:28 PM
I really hate how easy you're making this. I was finally going to get around to getting better with Eagle!

The only remaining reason for making my own board would be Arduino Mega compatibility and ability to directly connect to a basic LCD from the IO pins of the shield, adding buttons there. The I2C cable would get in the way of another shield, but I should be able to wire in a transistor in a way similar to the other SSR drivers (E to diode, B to DIO, C to SSR).

If I did use the mega, there are three serial channels (RX/TX pairs) available and plenty of DIO pins for a direct connection to an LCD.

Quote

The beauty of going the I2C route is that you get the temperatures, buttons, leds, and LCD all daisy-chained on the same two pins.


Ah yes - makes sense. So it adds the convenience of moving the LCD and buttons to one place and hiding the Arduino in another place. Like... under the drip tray in the electronics box!

Thanks again!
Edited by aindfan on 03/10/2011 7:28 PM
 
bvwelch
Top  #647 Print Post
Posted on 03/11/2011 12:23 AM

Quote

aindfan wrote:
The only remaining reason for making my own board would be Arduino Mega compatibility and ability to directly connect to a basic LCD from the IO pins of the shield, adding buttons there. The I2C cable would get in the way of another shield, but I should be able to wire in a transistor in a way similar to the other SSR drivers (E to diode, B to DIO, C to SSR).


You don't have to use the I2C connector if it gets in the way -- those same signals are available on J2 (stackable). Besides, as far as I know, the TC4 doesn't care about stacking order.

In theory the TC4 should work with the Mega. Haven't tried it though.
Edited by bvwelch on 03/11/2011 12:28 AM
 
aindfan
Top  #648 Print Post
Posted on 03/11/2011 9:01 AM

Quote

bvwelch wrote:
You don't have to use the I2C connector if it gets in the way -- those same signals are available on J2 (stackable). Besides, as far as I know, the TC4 doesn't care about stacking order.


Agreed - excellent point.

Quote

bvwelch wrote:

In theory the TC4 should work with the Mega. Haven't tried it though.


There is a physical mismatch - the I2C pins were moved on the Mega2560 from their A4/A5 spot over to pins 20/21 - see this image and note the group of communication pins. However, everything else is supposed to match up, and because of the size of the TC4, it would be easy to run a jumper wire from the I2C pins of the Mega back to the A4/A5 pins and to cut the header pin under the TC4 to disconnect from the Mega's A4/A5.

Thanks!
 
bvwelch
Top  #649 Print Post
Posted on 03/11/2011 10:04 AM

Quote

aindfan wrote:
There is a physical mismatch - the I2C pins were moved on the Mega2560 from their A4/A5 spot over to pins 20/21 - see this image and note the group of communication pins. However, everything else is supposed to match up, and because of the size of the TC4, it would be easy to run a jumper wire from the I2C pins of the Mega back to the A4/A5 pins and to cut the header pin under the TC4 to disconnect from the Mega's A4/A5.


That sounds like it would work fine. Also, you might be able to use a bit-banged version of the I2C library and not make any hardware mods. I did my early prototype work using the JeeNode which is all bit-banged I2C: http://bvwelch.co...

Edit: oops, that photo is a RBBB not a JeeNode, but I did a lot of testing with JeeNodes also, before deciding to go with the standard Arduino 'shield' form-factor.
Edited by bvwelch on 03/11/2011 10:07 AM
 
ginny
Top  #650 Print Post
Posted on 03/12/2011 2:17 PM
OK guys:

If I want to use my PowerBook G4 with one of these what is it I need. This particular Mac is running current software and would be dedicated to my roaster/s.

I would like to set it up with my Q3.

Thoughts please.

thanks in advance for responses!

ginny
Grin
 
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