View Thread

greencardigan wrote:

And here's the waveforms showing the ZCD pulse and OT2.

greencardigan wrote:

I think I have fixed my freezing/reseting problem. I did the following.
- Powered the arduino from a 7.5V DC power supply rather than USB
- Putting ferrite beads on most of the inputs to the Arduino/TC4
- Adding an X2 suppression capacitor across the 240V AC fan supply.

greencardigan wrote:
When i touch the roast chamber or braided thermocouple shielding, I sometimes get a sudden negative drop in the temp reading.

greencardigan wrote:Does this suggest I need to ground the thermocouple inputs? Maybe using the spaces left for resistors on the TC4 board?

Bhante wrote:

1) It would be useful to be able to separate the I2C lines from A4 and A5, as there are many new versions of the Arduino these days, many of which use different pins for I2C, and it would seem a pity to lock users in to old technology. I suggest a simple solder jumper connection on the circuit board, which uses very little extra space. As long as the chips on board remain connected to the I2C header on the shield, the SDA and SCL lines can then be disconnected from A4 and A5 and connected by jumper leads to wherever the appropriate I2C pins are. If real estate permits, you could put an extra 2-pin header hole for SDA and SCL adjacent to the I2C header to facilitate connecting the jumpers, or if space does not permit the wires will just have to be forked.

Bhante wrote:
2) Some boards use 3.3V instead of 5V. It would be worth giving a little thought to the implications of this, however it may not be serious - the Olimexino for example has both the Arduino 3.3V and "5V" pins powered with 3.3V, so with existing wiring the I2C header on the shield remain powered by 3.3V as required. Vin on the Olimexino can be anything up to 30V (the 24V battery on a heavy goods vehicle, for example), so in the case of the Olimexino we certainly don't want I2C connected to the Vin pin. As for other boards I don't know. With 3.3V boards the I2C chips on the shield can remain at 3.3V, while a little step-up board can be put in between the I2C header and the LCD to give the 5V the LCD probably requires.

Bhante wrote:

3) What about putting holes on the shield for an optional jumper to short the thermocouple contacts together, where particular channels are not used? Here it makes more sense to use a pin header type jumper rather than a solder jumper, so that it can readily be inserted or removed as required, instead of having to use a special external plug. What I have found implies that for example leaving channels 3 and 4 unconnected while using channels 1 and 2 will introduce errors on channels 1 and 2, even if only 2 channels are selected in the software (and likewise for channel 2 if using only channel 1). However I have only briefly tested the effect of setting the number of channels in the software so it is possible I could be wrong on this.

Bhante wrote:

4) You may remember I once suggested putting a couple of small holes (circa 0.5mm) on the edge of the board where the thermocouple wires come out from the screw connectors so that the thermocouple wires can be secured in place with a piece of nylon filament (fishing line etc). If the Arduino is mounted in a box with the USB socket accessible to the outside, and thermocouple sockets are also mounted in the box, then the wires from the TC4 to the thermocouple sockets necessarily have to bend very very sharply indeed coming out of the screw sockets. This puts an awful lot of strain on them especially when using braided thermocouple wire, and I find they come loose very easily. I find these tiny little screw clamps have great difficulty clamping the wires firmly, although it will probably depend on the type of wire and the number of filaments in the wire, size of wire etc. So I think it would be very helpful to be able to bind them in place with a little nylon filament.

Bhante wrote:

5) I would much prefer to have the thermocouples moved to any one of the other 3 sides of the board, but the conclusion last time we discussed this was that there is simply not the space available to achieve this; nevertheless I'll leave this suggestion here in case you think it makes sense to turn the bourd around. Putting the OT1, OT2, I/O3 connectors on the USB side obviously makes some sense for easy connections to the roaster and the thermocouples can then be on the opposite side, but that is only possible by changing the whole layout which you probably don't want to do.

Bhante wrote:
6) Just a wild idea - have you ever thought about a move away from the shield concept altogether? After all, since we are no longer using the parallel LCD pins, most of the Arduino connections are now through the I2C port, apart from the PWM pins and optionally the analog pins. Therefore instead of mounting the board on the Arduino as a shield you have it adjacent with a handful of pins coming out for I2C, PWM and analog, which can then be connected to whatever pins you like on the microprocessor. I am thinking of this from three perspectives: firstly this leaves more or even all the arduino shield pins free for any other shields you might want to connect (on some of the Arduino compatibles for example you can connect all the I2C, PWM and Analog pins you need to non-shield pins); secondly some Arduino boards and likewise some compatibles have certain incompatible pins such as I2C etc, and also boards like the Nano have their pins in completely different places; and thirdly the TC4 can potentially be used in many different ways with many different microprocessors, most of which do not have the Arduino form factor. There is no reason not to connect it to an STM32 Discovery board for example, if someone wants to modify the software and libraries or use completely different software.

JimG wrote:


Again, this is simply a matter of real estate. I liked the idea then, and still like it. But the shield would have to become bigger to accommodate.


In its present state the shield can be separated from the Arduino by using a 4-wire cable connected to the I2C header on the TC4. Use of the shield's input/output pins is lost, but the temperature logging capability is preserved since all of the IC's on the shield are I2C anyway.

Bhante wrote:
PS - if you put solder pads on the two holes for the locating pins of the thermocouple terminals, the terminals could optionally be turned around so that they point inwards! Not sure it is an ideal solution though, and might not work for the new 8-in-a-row terminals - how many locating pins do they have?

JimG wrote:
The 8-position terminals do not have locating pins.