Labview

I am currently working on a research project involving tactile sensing. My primary programming language is going to be National Instruments Labview and Matlab. I chose Labview because I have used it in the past and I also like their DAQs. I have a NI USB-6221 that we got funded through our student government. It looks very promising, but there is one major obstacle I have to get past: installing Labview.

I have installed Labview on my laptop in the past as well as our lab's desktops. There were no major problems back then. Recently, I decided to upgrade my laptop's operating system to Mircrosoft's Window 7. When I tried to install my copy of Labview 8.6 it gave me an error stating that I had an incompatible operating system. I decided to work around this problem by having using Window 7's "xp mode", a virtual system that runs Windows XP. Labview installed fine on that system, but the drivers for it could not properly operate the DAQ. I am very disappointed. I have yet to find a solution online and off for this problem. I may resort to installing Labview on my antiquated desktop.

Johnny Lee's Wiimote Whiteboard

I once stumbled on Johnny Lee's work while looking through TED talks. His presentation is one of the more memorable of what was offered at the time. The talk was all about using inexpensive equipment in order to achieve amazing effects. Using a $40 Wiimote, he was able to create applications comparable to high tech and high dollar devices.

It wasn't until I introduced Dr. Lee's presentation to a coworker, John, that I decided to embark on recreating and experimenting with one of Dr. Lee's projects: the Wiimote whiteboard. John and I decided that we would recreate and possibly improve on the whiteboard in order to present it in the annual Jagfest, which is an event held to inform and recruit freshman into joining clubs.

Since I'm an EE, it is natural that I will work on the hardware aspect of this project. So far I managed to create the infrared pen for this project. John has been tirelessly boring into code and perusing through apps to show off to the freshman.

I'll try to take pictures at the event and update on any additional hardware that we decide to fabricate.

Here are photos of the IR pen I made this evening:


I tried to make it look like an unmodified Sharpie as much as possible.

You can faintly see the glow of infrared light in this picture.

Battery Meter continued

I realized that I neglected to include some details about the design that will make it much easier for those using the previous post as a reference.

The pinout for the LM3914N is seen here:


Pins 1, 18, 17, 16 ... 10 correspond to the first, second, ... tenth LED.

LM350 is a adjustable voltage regulator. It works very similarly to the LM3914N. The desired output voltage is obtained by manipulating 2 resistors in a voltage divider configuration.

Here is the design soldered onto a protoboard.

Sadly the back isn't as attractive.
Hope this clears things up.

Battery Meter using the LM3914

I was asked by my superior to create a battery meter using the LM3914 by National Semiconductor to drive a set of 10 green LEDs that will light up from 12V to 13V.

I started out by checking out the datasheet. The example used on page 2 was fine and dandy for measuring a voltage from 0 to 5V, but for a battery meter I needed to measure the voltage starting at 12V and ending at 13V. I initially thought this would be a quick and easy assignment, and if it wasn't for a couple of naive mistakes, it would have been.

The trick with using the LM3914 is remember a couple of key points about its operation:

• The voltage between Ref Out and Ref Adj is kept constant at 1.25V. This means that the resistance between the two terminals(R1) will decide what current flows through that branch(R1 and R2).
• The voltage powering the chip must be 1.5V more than the upper limit of the signal voltage.
• The LEDs must be tied to V+ and the chip.

If I had known the forementioned facts, I would have saved myself a lot of headaches. After figuring out those tricks, its a simple matter of figuring out how to get 13V at RHi(Pin 6) and 12V at RLo(Pin 4).

The following schematic is the end product.


Note: Pin 9 is the "mode" pin. Either by tying it high or floating it, you can choose to display in bar mode or dot mode. The mode determines whether the LED array displays your voltage as a solid bar or a single dot. If you have a non-zero lower limit, you may split up R2, in my case R4, and treat it as a voltage divider to use as your lower limit if you are using dot mode. Otherwise, you must use an external reference because the current pulled into pin 4 in bar mode is far to large and will swing your lower limit around.

**Update**
A couple of photos of the schematic on a bread board.