Handle for I2C Devices

[Joey-1970]

Hello Joan,

here I again... ;-)

I try two I2C-Devices on the bus (BME280, BH1750). I expected one Handle for each I2C-device. But i get only one for them (or the same for each...). If I try only one to read, it works for both of them, but when I try to read from two, one dosen't work...

How does it work correct?

Joachim

[joan2937]

I can't tell without seeing the code you are using.

[Joey-1970]

Hello Joan,

thank you for your answer. My projekt ist here: https://github.com/Joey-1970/SymconModules

Let me explain you what I mean in principle: For example I take two BME280. I can choice the Device Address between 67H or 77H, but the register for measurementdata and calibratedata are the same! So when I "ask" for Handle with command, I need the Device Address for it. If I want to read or write I only need the handle and the register - not the device address! So, I wondering, how it can be possible to read with the same handle the same register...so I expeted one handle for each Device on the bus.

In my project I make a "interface" between a distant Raspberry pi with some devices and IP-Symcon, a software for smart home...

Joachim

[joan2937]

You need to post a complete example script which shows the problem. I need to see how you are opening the I2C devices.

[Joey-1970]

..the complete code is linked... ;-)

In the projekt, there are to Client Sockets, one only for commands, one for Notifications. For the next steps., I only use the Command-Client Socket I try to explaine it:

1. If some add a new device, he has to give so informations, for example the device address
2. I catch the handle for this device: CommandClientSocket(pack("LLLLL", 54, 0, $data->DeviceAddress, 4, 0), 16); and give it back reserved for this device
3. I read something CommandClientSocket(pack("LLLL", 61, $data->Handle, $data->Register, 0), 16); or write something CommandClientSocket(pack("LLLLL", 62, $data->Handle, $data->Register, 4, $data->Value), 16);
4. If someone add a new I2C-Device I do it the same way --> 1. But if I do it in this way, I get for each Device the same Handle...

Maybe it is because I use the Command-ClientSocket which is closed after data-transmission?

Joachim

[joan2937]

You need to prepare a small complete example I can run which demonstrates the problem. I'm not prepared to spend a lot of effort on something unless there is a demonstrated problem.

[Joey-1970]

...send two times a Command 54 to get a free handle with differnt device address?? CommandClientSocket(pack("LLLLL", 54, 0, 67H, 4, 0) CommandClientSocket(pack("LLLLL", 54, 0, 77H, 4, 0)

[joan2937]

I don't know what you are doing wrong. I can do the same from the command line without error.

$ sudo pigpiod
$ pigs i2co 1 0x67 0
0
$ pigs i2co 1 0x77 0
1
$ pigs i2co 1 0x78 0
2
$ pigs i2co 1 0x79 0
3
$ pigs i2co 1 0x7a 0
4
$ pigs i2co 1 0x66 0
5
$ cat /dev/pigerr&
[1] 1847
$ pigs csi 4
$ pigs i2co 1 0x60 0
6
$ 2016-08-04 20:08:46 i2cOpen: i2cBus=1 i2cAddr=96 flags=0x0

$ pigs i2co 1 0x50 0
7
$ 2016-08-04 20:08:59 i2cOpen: i2cBus=1 i2cAddr=80 flags=0x0

[SlySven]

You say you have two of each of these devices - are all their I²C addresses configured correctly? Looking at the data-sheet for the BME280 on page 31 it says that the I²C address is 0x76 if the SDO pin is tied to ground and 0x77 if the pin is tied to V_DDIO. Similarly from the BH1750 data-sheet (:thought_balloon: Humm, I think I have a strip of 5 of those somewhere... ) on page 10 it says that with the ADDR pin grounded ( < 0.3 * V_cc ) the address is 0100011 or 0x23 and with it at a high level ( > 0.7 * V_cc ) the address is 1011100 or 0x5C.

Now if you are using two BME280 at the same time on the same bus they must be set to have different I²C address - one must have the SDO pin pulled low and the other pulled high - then the one with the low SDO pin will appear at address 0x76 and the other one with it high will be at 0x77. It doesn't matter from a circuit point of view which is which (the same is true for the other pair of devices)...

{Though you or your system's user will want to know where the module with each configuration is - so they can tell whether the cold dark place with no atmosphere is somewhere outside or in your front room :laughing: }

[Joey-1970]

Hello SlySven,

thanks for your answer, but I know this and this is not the problem.

Hello Joan, your are right! I make a simply test-code, where I only want to catch two different handle for two device. I look in my code again and I can fix the problem - but I don't understand why this cause this error. I do this: Every time the user change some settings and press "Apply" the code catch a new handle. So the number of handle went higher and higher - but it works. So I think, it will be a good idea to delete curent handle (is there a guilty one) and get a new one. But if I have more then one I2C-device it won't work. Both devices get back a "0" as handle. Maybe this is an timing problem, At this time I don't know ist. For now, I don't delete the current handle and it works. Here, special thanks for your patience!;-)

The BME280 works in my code, I now work on implented the PCS8591 and the Nextion NX4832K035 Touchdisplay on the serial port.

It is possible and meaningful in your opinion to make a function like "I2cdetect" do?

Joachim

[joan2937]

You can have many handles to the same device at the same I2C address. There is no point in doing so though. Generally you should get a handle for a device just once at the start of your program and release the handle at the end of the program.

The following script does a simple I2C device detect.

#!/usr/bin/env python

# 2015-06-30
# i2c_detect.py
# Public Domain

import pigpio

pi = pigpio.pi() # connect to local Pi

for device in range(128):

      h = pi.i2c_open(1, device)
      try:
         pi.i2c_read_byte(h)
         print(hex(device))
      except: # exception if i2c_read_byte fails
         pass
      pi.i2c_close(h)

pi.stop # disconnect from Pi