Hall effect sensors (by alaric)

At the Bristol Hackspace this evening, I powered up a Hall sensor.

The Allegro A1321 takes a 5v supply and outputs 2.5v - plus or minus 5mV per gauss of magnetic field in the sensor.

It turned out that small magnets don't produce many gauss, so I added a 741 op-amp with a gain of about 100 to get more useful output voltage deflection!

Here's the experimental setup:

WIth no nearby magnets, we read about 3v:

But with a very nearby magnet, we get a large deflection, which drops as we get the magnet many cm away, but is still significant:

Clearly we still get significant readings a good distance away, and the nonlinearity isn't too bad; it doesn't max out with the magnet very close but still varies many cm away.

For my next trick I'll make a few of this circuit on some veroboard and hook the outputs up to an AVR with several ADCs that I have lying around, and try comparing the results to measure position (and maybe orientation?) of a magnetic probe...

Monster Painting (by sarah)

This is what I have spent my child free morning on :/

Click on the images if you want to see them larger.

They are for a Halloween art exhibit at Center Arts.

Mary Learning (by sarah)

Mary loves textures and manipulating things with her hands - she can't put the rings back on the pole yet but she loves tipping them off or lifting them one at a time and playing with the rings.

We also have film night once a week and this is a cute pic of her sitting on the settee joining in 🙂

Icicles (by sarah)

This is a photo from last winter - I just really thought I should share these fantastic icicles!

The Piggies (by sarah)

I found this cute picture of Jean holding the guinea pigs. They are sadly no more but were well loved whilst we had them.