[sdiy] Hall Effect transistor question

[Michael Bacich]

Hello Harry and Ian,

I just wanted to thank you guys for your helpful tips last month on  
working with the linear Hall-effect sensors.  There was such a sensor  
in the throttle of the electric scooter I was trying to repair.  As  
it turned out, the scooter's no-go problem was indeed a result of a  
failed Hall-effect IC, and I was finally able to get a perfect  
substitute for the original part from Allegro Semiconductor.  In  
fact, they sent me a handful of free samples, so I've got some extra  
ones now to play with.  I'm not sure what I'll do with them yet -- a  
potless CV or wah pedal comes to mind.  Anybody have any other ideas?

The part I ended up using is an Allegro A1302EUA "continuous-time,  
ratiometric, linear Hall-effect sensor".  Allegro also has the  
A1301EUA, which has a different sensitivity (higher sensitivity, I  
think) to magnetic fields.  They are little three-pin mini-SIP  
devices, and look just like small transistors.  They cost about a  
dollar each in small quantities, although none of our usual suppliers  
seem to have them in stock these days.  The connections couldn't be  
any simpler:  Ground, + Supply, and Output.  Internally, the device's  
output is a simple emitter follower.  The output is proportional to  
the device's proximity to a magnetic field.   This field can be  
easily provided by small permanent magnets placed near the IC, or a  
field from a nearby electromagnet, such as an energized motor coil.

I don't know what killed the original one in the scooter -- It didn't  
happen while operating the machine, but probably happened while I was  
messing around with the wiring (without a schematic, of course!).  I  
may have inadvertently shorted the wrong pin directly to the 36 Volt  
supply or something like that (the Hall-effect device's upper voltage  
limit is around 6 Volts or so).

Michael Bacich


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