Surprise! Surprise! I received the boards from the PCB house today(05-Jan-2015). I submitted these boards online on 21-Dec-2014 and received a notification that the boards are made and they are about to be dispatched via the standard international post on 27-Dec-2014. The whole process took just 2 weeks. Previously, my boards get stuck in the post for weeks and I didn’t anticipate them to arrive until at least the 2nd week of January, but hey! It took just 9 days, this is the best so far.
I quickly gather all the needed components to have one board made and here it is!
There isn’t much space available on the T-962 between the controller board and the heat shield. (T-962A should be OK) I need to do several modifications in order to have this piggyback fitted to the controller board and still be able to replace the top of the case without punching a hole into the heat shield.
The first thing I need to do is to replace the two existing reservoir capacitors with the low profile type so that I can sit the board lower, without the bottom of the TC board touching the components. The next step is to remove the original green terminal blocks for the thermocouples since I no longer need them any more.
With the three tallest components removed/replaced, I no longer need to worry about the underside of my TC board in contact with the components underneath. If I had the bigger T-962A oven, I needn’t have to replace the capacitors or removing the green screw terminals, I just use taller standoffs to have the board stand just clear the top of the tallest components. Currently, I’m using two 14mm standoffs. I also put a layer of Kapton tape on the bottom side of the thermocouple board just in case.
Although not straightly necessary, I like my board removable, so I use sockets and headers for the connections. This give me more flexibility should I need to swap the board later on.
At the other end of the headers, I soldered the wires to the main controller board. The purple and yellow wires connect to the SCL and SDA pull up resistors. The green wire connects to the ADO pad on the controller board, with the latest firmware, you can control the system fan using this pin. The black and grey wires are just ground connections. Although not shown in the picture, I hot glued the wires onto the controller board so that there will be no strains on the solder joints. Here is another close up
Finally, the top JST socket(the white sockets) on the TC board receive power from the original system fan, (socket above the white opto-isolator) it’s about 9VDC.
The original system fan will go into the bottom JST socket, which is now under software controlled via a n-channel FET. (Q4 in the picture)
So here it is, with all the cables plugged in and before I put the top back on.
After I double checked the connections, I flipped the power switch and everything works as it should be. No more scorched PCBs!
In the next post, I’d have the multi-channel version ready to make full use of the firmware, which supports 4 thermocouple channels.