In one of my past posts, I’ve try to use 2 identical I2C devices on the same bus. Mario Vernari who help me for another problem on my Lego city and with whom I’ve exchange a bit to find other solutions help me there two. Mario is coming from the electronic side and I come from the software side. So he can correct me when I’m wrong with my electronic . And I was quite wrong with the previous solution trying to switch on and off the power of the sensors. Mario gave me couple of good reasons:
“First off, any silicon embeds diodes, thus -even unpowering a device- there's a non-zero current flowing into. In this case, through the SCL/SDA lines, via pull-ups.
Secondly, you're using sensors, and they typically need a certain time to settle their internal state, reach the steadiness, etc. There are also "smarter" sensors, which perform a kind of auto-calibration when they are powered up. If you switch off, you'll lose those benefits.”
And he gave me a tip: “use a 74HC4052”. So lets go and see what it is. It’s a switch for analog signals. You have 4 inputs (named Ya, a = 0 to 3) and 1 output (named Z). But they are 2 ways. So when you have selected one line, you can send signals in both ways. And there are 2 of those in the chip (naming will be nY and nZ, n = 1 and 2).
That allow to switch the overall SDA and SCL bus to the right sensor. And this will allow to pilot up to 4 identical sensors. The selection of the line is made by the S0 and S1 with the following rule:
So regarding the code I wrote for the previous post, it will remain the same! It will work exactly the same way. What is changing is the electronic part. And here is the new design:
Mario also give me the following advice: “Note that when you cut off a device, you should provide the pullups anyway”. So That’s what I did by putting the pullups for each component.
Now it’s working and much better as the line switch is really fast and there is no need to wait for a long time to read the data. So thanks Mario for the tip!
Long time ago, when I was doing lots of demos and used to have to display mobile phone like smartphone of Windows Embedded devices, I needed a mobile video recorder to be able to display them. Of course, I though using a webcam but the webcam alone does not allow you to demo the device. And I figure out that those kind of animation stand costs lots of money and were not easy to transport and very costly to rent. So I decided to build my own. And I recently use it again as I had to demo my Windows Phone 7 device and also .NET Microframework device like netduino.
The main features I needed were:
So I came to the following solution:
Everything can be unplugged and transported easily. It is using a webcam and simple plastic pipes. It costs only couple of euros ($ for our non European friends ) to build. On the software side, I used a DirectX sample which I customize to create my own application.
And I sued this solution very recently during the French TechDays where I did a demo of .NET Microframework. The equipment in place was not working and I was glad to have my own mobile video recorder with me So, I use it as you’ll be able to see when the video will be available.
so let start with the hardware part. what you’ll need:
Now to build it, you’ll need to cut the following parts:
And here is the technical schema (forget about the webcam yet):
With this you can basically adapt any camera. You may recognize on this picture an old Philips webcam and on the one I pick recently a nice Microsoft LifeCam Cinema. A perfect HD camera with some good feature to tune the brightness. Also, it is very easy to install the camera on the pipes.
Step 1: glue assembly
Step 2: soft assemblies
On the software side, I’m using a simplified version of the DirectX SDK AMCAP example. You can easily select the webcam you want (if you have an integrated webcam and the external one, make it easy to choose) and setup the settings in the capture filter like the autofocus, the resolution, etc.
If you want this software let me know and write me at firstname.lastname@example.org.
I hope you’ve enjoy this tutorial to create hardware which is not electronic this time