Home Automation


Overview Hardware Software Applications






Quantum Research Group makes these chips that are designed to detect proximity. They're used in control panels to replace mechanical buttons, fluid level sensing applications, and anywhere else you might want to sense proximity. They're basically capacitance sensors, and the company has an easy to understand document about how they work.

On the right is a qt310 which has a single channel. [Quantum makes devices that support up to 64 channels.] You can see from the picture that the only external components that were required for this thing to work were two resistors, and two capacitors. I was using that green coiled jumper as my sense electrode, and you can see the probes of the meter connected to ground and the output pin of the chip.

I powered everything up, and it worked on the first try. The meter reads ~5V normally, and when I bring my finger close to the coil it drops down to 0V.

I bought a handful of these chips. The six channel version I'm planning on using to build a control panel for the office. The first application of the single channel version is going to be detecting the presence of someone sitting on the couch. Anything conductive can be used as a sense electrode, and since the couch has a pull-out bed I'm hoping to connect the chip to the steel frame and turn on the touch screen on the end table when someone sits down.

Programming the qt310

The chip has many user-programmable features that relate to how the chip senses, the behavior of the output pin, how and when the chip recalibrates itself, whether or not it outputs a heartbeat signal...

One of my problems is the chip's Max On Duration feature. If the chip senses for longer that this duration it recalibrates itself. This is a problem for me because I'm assuming that people are going to want to sit on the couch for longer than this. Fortunately this feature can be turned off with PC software, but it requires an interface board. [For the adventurous, Quantum provides information on how to program the chip without this board.] 

I'll update this when I get the board and actually get the couch sensor working.

Update: Well, I got the board. It's very well made [it had better be for $50], and works great. But I can't seem to be able to get the chip to work with the couch frame as the sensor. I'm not going to put much more effort into it as I'll be replacing the couch soon and I'll need to come up with a different sensor for that. Probably something like a window screen under the cushions.

qt310_bb.jpg (186729 bytes)
The qt310 chip on a breadboard. [Click to enlarge.]