Im a total newbie, no prior knowledge.
Through I2C you can read-out up to eight sensors by setting individual addresses. Can you just interconnect separate sensors (piggy-back, serial) using the two connectors on board ? Using what cabling ?
Thank you very much,
Jan
Hello @j.baijer,
Yes, BUT it’s a two-step process:
- You must set a unique address for each board. This is done by adding or removing solder jumpers as suggested in this picture.
- You must change the code so that you are addressing the associated board. According to the Adafruit literature:
The default address is 0x18 and the address can be calculated by ‘adding’ the A0/A1/A2 to the base of 0x18
A0 sets the lowest bit with a value of 1 , A1 sets the middle bit with a value of 2 and A2 sets the high bit with a value of 4 . The final address is 0x18 + A2 + A1 + A0 .
So for example if A2 is tied to VDD and A0 is tied to VDD, the address is 0x18 + 4 + 1 = 0x1D.
If only A0 is tied to VDD, the address is 0x18 + 1 = 0x19
If only A1 is tied to VDD, the address is 0x18 + 2 = 0x1A
If only A2 is tied to VDD, the address is 0x18 + 4 = 0x1C
Recommendations:
- Get a single sensor working.
- Solder the sensor to a new address and then get that to work.
- Get two sensors working.
- Rince and repeat until everything is working.
Please let us know if you have additional questions.
Sincerely,
Aaron
2 Likes
Thanks Aaron for this clear explanation. For this particular board, what would be the size of these 10k SMD ? Do you advise against just creating à solder bridge ?
Thanks again !!!
Jan
Sorry, should have been more precise … What would be the reference to order from DigiKey ?!
Hello Jan,
Judging from the 0.1" pitch on the through holes, the resistors should be about an 0805 size. So one option would be 541-10KACT-ND. These are 0805, 10K, 5%, 1/8W.
You can purchase them in any quantity, down to 1 piece.
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Hi j.baijer,
There are two different versions of MCP9808 boards offered by Adafruit – the standard 1782 version and the STEMMA QT 5027 version.
For the 1782 version, rather than adding or removing resistors, one would simply apply Vdd to the appropriate header address pins, A0, A1, A2, on the board to set the respective address pins to logic high. The three 10k pull-down resistors will otherwise pull the address pins to ground, setting the respective pins to logic low.
See the following schematic for the 1782 (I added the dashed green lines and circled resistors to show connections):
For the STEMMA QT 5027 version, rather than applying Vdd to header address pins to set them high, you short the respective shorting pad on the rear of the board, which connects the respective address pin directly to Vcc. One could solder zero-Ohm jumper resistors onto these pads, but I would recommend just adding solder bridges. If you need to remove it later, a little desoldering braid will do the job.
STEMMA QT 5027 board
See the following schematic for the STEMMA QT 5027. Note that the shorting pads, when shorted, connect the address pins directly to Vcc. Otherwise they are pulled to ground via the 10k Ohm resistors.
3 Likes
Thank you @David_1528.
Thank you so much APDahlen and David, thanks to you I feel more confident !
Jan
1 Like
Absolutely, @j.baijer.
Please let us know when you successfully finish your project.
Happy soldering,
Aaron