SHT31 evaluation + second proofing expansion board

hujj

SHT31 evaluation + second proofing expansion board [Copy link]

 

Now it is really convenient and fast to sample PCB boards. I received the modified SHT31 expansion board in just three days. The following is the expansion board after the second sample:

This time, the reed for picking up the signal did not use the copper pins in the header. Instead, the copper wire removed from the RJ45 socket was used to connect the sensor's I2C pin.

Carefully remove the copper wire inside:

I originally planned to straighten it and then bend it as needed, but it broke unexpectedly. I had to follow the original shape and only change the soldering foot part. The remaining three copper wires were just used for the SDA, SCL and GND signal lines.

First, use engineering double-sided tape and transparent tape to fix the copper wire for welding:

Then adjust the position carefully:

The connecting reeds of other signals are also replaced with the reeds removed from the USB socket:

First, solder the reeds one by one:

Then cut off the excess part according to the actual situation and bend the end slightly to facilitate contact:

The retaining spring for fixing the SHT31 evaluation board is made of copper sheets removed from old sockets. It is thinner than the original 0.5 thick copper sheet and has better elasticity:

Below is a comparison of the two expansion boards. The top one is the first one, and the bottom one is the current one:

During production, it was discovered that there was still an error in the expansion board, that is, the position of BKGD of ST2 was reversed. Fortunately, the LCD display part is not involved at present, so only the PCB file was modified and no re-proofing was required.

After the expansion board is initially completed, I can't wait to test the effect. The first step is to use a logic analyzer to check the I2C signal:

Connect the SCL, SDA and GND signals:

Observe the nRF51822 reading and writing data to the sensor. This is an operation of reading 6 bytes first and then writing two bytes:

Preliminary analysis shows that the first 3 bytes read should be the humidity data of the sensor, and the last 3 bytes are the temperature data. The function of the 2 bytes written is not clear for the time being.

From the captured I2C clock, it reaches 363.6kHz, which is still relatively high:

In addition, the RX, TX, SWDCLK, SWDIO and other pins of ST1 were tested, and no level changes were found:

At this point, the production of the expansion board has come to an end. The next step is to try to use ST-LINK to see if I can download the burning program. The manual says that I can use J-LINK to download, but I only have ST-LINK, so I don’t know if I can download it successfully.

dcexpert

Why not use pogopin? It comes in many specifications and is more convenient and reliable than the reed of the crystal head.

hujj

I don't know if there is such a device. I'll search on Taobao.

hujj

After searching online, I found that the contacts for ST1 and ST2 are very suitable, but I couldn't find a suitable device to connect the sensor I2C connection. The center-to-center distance of these four contact points is only 35ml, which is equivalent to 1.4mm. The width of the contact points must be less than 1mm.

dcexpert

hujj posted on 2020-1-8 21:08 I searched online and found that the contacts of ST1 and ST2 are very suitable, but I didn’t find a suitable device for connecting the sensor I2C connection. The four contacts are...

1mm pogo pins are hard to find because the spacing is too small, but there are many 2.54mm ones.