Tuesday, October 06, 2009

I had a little time to experiment with a new project. I'm working on using a Freescale pressure sensor to measure the specific gravity of a liquid. This is a piece of a larger project that I'm working on, but I need to research this before I work on the rest of it. More on that later.

Pressure in a liquid follows this formula:
p = ghd
where p = pressure, h = height of liquid above sensor, g = acceleration of gravity, d = density of liquid

So using a differential pressure sensor (MPVX5010DP) from Freescale, I can get all of the values in the formula and solve for d. The physical test setup is show in the picture below. Basically I have lengths of plastic tubing of two different lengths attached to the sensor's pressure ports (make sure to get the right tube to the right pressure port; pressure port 1 always have to have a higher pressure on it than pressure port 2; check the datasheet). The tubes are then tied to a steel ruler with the tube ends a fixed distance apart (in this case 4" apart).

It seems like the pressure reading does indeed change with the density of the liquid the probe is placed in. However the difference in the readings is fairly small. This tells me a couple of things:
1) I should increase the distance between the end of the tubes (essentially increasing "h" from the formula before). This should increase the magnitude of the voltage read from the sensor, thereby amplifying the sensor voltage. Eight inches between the tube ends should be good. 2) Since I'm eventually going to be reading the sensor voltage using a microprocessor's ADC, I can decrease the voltage range of the ADC to increase the resolution of the ADC readings. Based on my final application, I'm going to set the voltage range to 0-1.1 V.

Here is then data I got with several different sugar solutions:

Hydrometer Reading -> Sensor Reading
1.000 -> 707mV
1.036 -> 723mV
1.068 -> 734mV

Monday, August 17, 2009

I finished Nadia's desk a few days ago. The MDF sealer worked like a charm. Here are some pics.

Monday, July 20, 2009

I'm just about done with the desk I've been building. The only thing left to do is putting a couple of coats of paint on it.

I ended up making the desktop itself out of MDF since it is stable, flat, and heavy. I routed some nice edges on the desktop but I've been having trouble painting the routed edges because they're so porous. I found a recipe online for a sealer made from 4 parts water and 1 part wood glue which should fix that problem. I'll try that out tonight.

I'll post pictures as soon as I get the desk done (hopefully this week).

Thursday, June 25, 2009

I've been looking into a new feature for my DVR PC: Boxee. Boxee is basically a media client which makes it very easy to watch streaming media (pandora, youtube, hulu, etc.). I've been jealous of my Linux and Apple-wielding brethren, as they've had Boxee support for some time now. But the Boxee folks have finally put out a public alpha for Windows. It's a little buggy (it is an alpha after all), but I've been playing with it and it has lots of potential. I think I'll definitely be installing it on my DVR PC once it becomes a bit more stable.

I even found a forum posting about how to use a Hauppage IR remote to control it (which is what I currently use to control GBPVR).

Also, I think Netlfix and Boxee are working together to create a Boxee app to allow viewing Netflix streaming content, which I'm really psyched about.