I have two QWiic sensor boards (a SEN-Spectral UV Sensor AS7731) and an (SEN-29211 Ambient Light sensor VEML-7700) that want to connect together (WITHOUT the use of a Qwiic jumper). I want these boards to be on a single prototype board about less than 1" apart. I will be driving these with a Flipper Zero. How do I connect these two boards?
Use the 3v i2c3 SDA & SDL lines on the bottom half here
and wire them to the PTH holes here Hardware Overview - SparkFun Ambient Light Sensor - VEML7700 (along with power and GND)
Then use a qwiic cable to daisy-chain the 2nd sensor, communicating with both via i2c
You may or may not need to disable one sensor board’s i2c pull-up resistors (leave the other sensor’s active) if you can’t get steady data once all hooked up…their combined pull-up resistance may be too high by default, you won’t know for sure until testing with i2cdetect and getting some data going
Thank you fot the information. However, this is not what I asked.
I don’t want to use a Qwiic cable because the distances are very short. I just want to hardwire the two boards together. Perhaps you can answer this question: is the Qwiic cable 1:1. That is, is pin 1 (one end) connected to pin 1 (other end), for all the pins, or is there a crossover in the cable?
Another question. What is the address of the VEML7700 board? How can I change it?
I have never worked with I2C boards.
Steve
That won’t be an issue
The cables do have a twist (if you look in the photo from the link above you can see the connectors are facing opposite directions…you can see pins on one but not the other, which makes both ends effectively the same pin pattern when inserted); for i2c/qwiic the data and power lines are in fact 1-to-1…to daisy chain with hardwire you just jump one SCL to the other, same for SDA, power (3.3v) and ground
The VEML7700 communicates over I2C and has a 7-bit unshifted I2C address of 0x10
For the 7331 it is 0x74
All of these answers didn’t address the original question. However I found the answer: The 1 wire system is just a serial bus (using 3 lines, serial data, serial clock and ground, which can be extended and daisy-chained, just like any other bus. Because the bus is high-speed serial, extending the bus long distanceds (probably more than a few feet) necessitates high-speed bus drivers, bus receivers and proper cabling (shielded or twisted pair) between the bus drivers and receivers. I once had a problem with noise getting into a 16 bit bus between a microprocessor board and a memory board, and causing the program to go into never-never land. Solved the problem by using bus drivers, bus receivers, and shielded twisted pair cable.