8 to 12 magnet PAS

[dwvl]

The two Raleigh Arrays in my family have a PAS sensor that directly senses the teeth on the front chainring. So about 42 "magnets". These bikes are a real pleasure to ride; presumably the PAS arrangement helps with the fast and smooth pickup.

I'd really like to find a source for those chainring PAS sensors, but so far I've drawn a blank

 

[danielrlee]

The two Raleigh Arrays in my family have a PAS sensor that directly senses the teeth on the front chainring. So about 42 "magnets". These bikes are a real pleasure to ride; presumably the PAS arrangement helps with the fast and smooth pickup.

I'd really like to find a source for those chainring PAS sensors, but so far I've drawn a blank

What about using something like this to detect the chainring teeth:

https://www.ebay.co.uk/itm/M18-8mm-DC-5V-NPN-NO-LJ18A3-8-Z-BX-5V-Inductive-Proximity-Sensor-Switch/113223650675?hash=item1a5ca7cd73:g:pFkAAOSwPPNbhRS3:rk:3:pf:0

It works on a 5V input and detects aluminium and iron from a distance of 4mm.

 

[dwvl]

What about using something like this to detect the chainring teeth:

Interesting, thanks. Unfortunately a PAS sensor needs to be a "dual" device so that it can sense whether the chainring is going forwards or backwards.

 

[wheeliepete]

a PAS sensor needs to be a "dual" device so that it can sense whether the chainring is going forwards or backwards.

Never really thought too much about this, but now does the controller know which way the crank is turning? Where does the "duel" bit come from with a 3 wire sensor, positive, neg. and signal? Isn't it just a 3 pin hall sensor?

 

[danielrlee]

Never really thought too much about this, but now does the controller know which way the crank is turning? Where does the "duel" bit come from with a 3 wire sensor, positive, neg. and signal? Isn't it just a 3 pin hall sensor?

The controller doesn't know, but the sensor does.

Inside a 3-wire dual hall PAS sensor is a pair of hall sensors spaced much closer together than the magnet spacing and some basic logic processing circuitry. This is used to calculate the direction of movement and limit the output to a single direction of rotation.

 

[vfr400]

Single hall sensors switch according to how they cut lines of magnetic flux. They only switch if you have the right polarity and the right direction, but passing a South magnet from the left, it's the same as passing a North one from the right, which is why pedal sensors reverse direction when you reverse the magnet disc. You can therefore instal a single hall on either side as long as you use the magnet disc the right way up.

 

[Laser Man]

What about using something like this to detect the chainring teeth:

https://www.ebay.co.uk/itm/M18-8mm-DC-5V-NPN-NO-LJ18A3-8-Z-BX-5V-Inductive-Proximity-Sensor-Switch/113223650675?hash=item1a5ca7cd73:g:pFkAAOSwPPNbhRS3:rk:3:pf:0

That's quite a good idea. You would need two of them and a bit of logic circuitry to get the direction sensing, but they are certainly cheap enough.

 

[vfr400]

"As it is capacitive type proximity switch, its detecting object target is not limited to only conductor, but also liquid and even powder things, like plastic, water, glass, oil, etc. "

That will be fun when it starts raining!

Of course, as an alternative, you could always use a microphone and shout at it that you're pedalling to start your bike.

Normal pedal sensors work perfectly. Why would you want anything else?