Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Linear Hall Effect Sensor circuit help

Status
Not open for further replies.

Burtmeister

New Member
Hello, I am new to these forums and I hope I'm posting this in the correct area. I also hope someone can help me out with this circuit. I've always been interested in electronics, but I only know enough to be dangerous. Here's a little background on this question. I have an electronic drum set. In this set there is a module that is connected to all the pieces of the drums (triggers). One connection is a hihat pedal. This pedal is connected to the module with a 1/4" mono patch cord. The pedal itself is just a potentiometer which the module reads to determine how the hihat sounds. Where the pedal has a potentiometer in it and the pedal is pushed quite often the potentiometer tends to wear out pretty quick.

So I have an Allegro 1302 Hall Effect sensor that I want to use in place of the mechanical potentiometer. I will be placing the sensor under the pedal and a magnet will be attached to the pedal. That's the simple part. Where I'm stumped is how I connect it all together. I've taken some measurements. I have a a voltage coming out of my module for the hi hat control at 3.5V and normally that travels through my potentiometer hi hat pedal back to the module. The resistance of the potentiometer goes from 0k to 67k. If I want to use a hall effect sensor in place of the potentiometer pedal would I connect the output ground of the sensor to the ground of the module h ihat control, and to the ground of my separate 5v powersupply for the sensor? And then connect the positive output of the sensor to the positive of the hi hat control. And then the positive of the separate power supply to the positive input of the sensor? Can I just hook it up this way and go? The fact that there is a 3.5V already running through the pedal I'm worried that the 5V from powering the sensor is going to cause a problem. Any help would be greatly appreciated.
 
Buy a better pot... Do you know the manufacturer and part # of the current pot?
 
The output of the hall effect device would likely be very non-linear with respect to the magnet position. If you want to use it, I suggest some tests with a magnet and the hall effect to see if you can find a position of the magnet that will give you a reasonable linear output of hall effect voltage with petal position.

It probably would be a lot easier if you used a contact-less rotary shaft encoder such as **broken link removed** instead of trying to use the hall effect device.
 
The rotary shaft encoder sounds like a good idea. You can couple this to digital potentiometer that has up/down inputs and it might work with some glue logic. Digiatl POTS have restrictions on power up. Here are some 32 step 50K and 100K digital pots: **broken link removed**

Making them work may be tough. Other manufactures make them as well with more steps than 32. Quadrature outputs like you can get from an encoder. Here is a list of some shaft encoders. Encoders | Digi-Key

Digital pots have lots of restrictions on use and it will take some designing to make one work with an encoder. Power sequencing and current handling are other issues that need to be worked out.
 
The rotary shaft encoder sounds like a good idea. You can couple this to digital potentiometer that has up/down inputs and it might work with some glue logic. Digital POTS have restrictions on power up. Here are some 32 step 50K and 100K digital pots: **broken link removed**
You don't need the digital pot with the encoder I referenced. It has an analog output, which should be able to substitute directly for the present pot's output (perhaps with some buffering to get the correct voltage level).
 
Carl:

What a unique chip. I'll have to spend some time looking over the 36 pages of data.

Can you think of some ways to do resistance simulation in general?

In any event, short circuit current and open circuit voltage (pot disconnected) would be the first terms to know and whether or not what is to be simulated is 2 terminal or three.

I have a project that I'd like to do which is similar to the OP's and occaisionally I see people wanting to change resistance control to a 0-5V or some such signal.

The OP would still have to do the same. Convert an analog voltage to a resistance. In the OP's case, it's probably linear. We also don't know if its part of a gain block or whatever. I know you can buy motorized potentiometers that can use process signals to move it.

If your working with a control signal, you might be able to:
Sink a current with a FET until the voltage is X for each pair.
If the OP's pot is used in a gain block, it might be tougher substituting anything.

In a project I would like to do and you might think I'm crazy is to: substitute one thermister probe for another. I think the thermister is about 5-10K at 25 degrees F and I think the voltage applied is close to 5V. There is a micro switch that's activated when the probe is inserted. I don't have the schematic of the device. It's a microwave. I have to fix the convection/microwave first without a schematic. I just love the old thing. Somewhere I have the curve of the bad thermister. That's lost too.

So, I was thinking of using a high or low side current sensing IC and a FET to sink current. And to use a processor to read the new sensor and convert it to the new resistance.
It's limited range, like 115 to 200 F or so. I would like to be able to lower the limit too as well even if it is rarely. I need about 90F minimum for proofing yeast. Something I don't do often.

I just haven't done any measurements or experiments to figure out what I need to do.

---OP---

The OP's problem may be similar.

For the OP:
1. Is the potentiometer 2 or 3 wires?
2. What is the open circuit voltage?
3. What is the short circuit current?
4. Is there a relationship between the angular position and the terminal voltage?
5. Minimum? Maximum?
6. What's available to power the interface circuit?

67K is an ODD value.
 
Last edited:
Carl:

Can you think of some ways to do resistance simulation in general?

In any event, short circuit current and open circuit voltage (pot disconnected) would be the first terms to know and whether or not what is to be simulated is 2 terminal or three.

I have a project that I'd like to do which is similar to the OP's and occasionally I see people wanting to change resistance control to a 0-5V or some such signal.

The OP would still have to do the same. Convert an analog voltage to a resistance. In the OP's case, it's probably linear. We also don't know if its part of a gain block or whatever. I know you can buy motorized potentiometers that can use process signals to move it.
What type of resistance simulation are you needing? Certainly LTspice can simulate just about any manner of resistive circuit.

Why do you need short circuit current and open circuit voltage? All you need are the pot output voltages over its rotational range and the input impedance of the circuit the pot wiper goes to (assuming it's operating as a normal voltage divider potentiometer with one leg grounded).

Don't understand what you mean by "Convert an analog voltage to a resistance."?
 
Carl:

What a unique chip. I'll have to spend some time looking over the 36 pages of data.

Can you think of some ways to do resistance simulation in general?

In any event, short circuit current and open circuit voltage (pot disconnected) would be the first terms to know and whether or not what is to be simulated is 2 terminal or three.

I have a project that I'd like to do which is similar to the OP's and occaisionally I see people wanting to change resistance control to a 0-5V or some such signal.

The OP would still have to do the same. Convert an analog voltage to a resistance. In the OP's case, it's probably linear. We also don't know if its part of a gain block or whatever. I know you can buy motorized potentiometers that can use process signals to move it.

If your working with a control signal, you might be able to:
Sink a current with a FET until the voltage is X for each pair.
If the OP's pot is used in a gain block, it might be tougher substituting anything.

In a project I would like to do and you might think I'm crazy is to: substitute one thermister probe for another. I think the thermister is about 5-10K at 25 degrees F and I think the voltage applied is close to 5V. There is a micro switch that's activated when the probe is inserted. I don't have the schematic of the device. It's a microwave. I have to fix the convection/microwave first without a schematic. I just love the old thing. Somewhere I have the curve of the bad thermister. That's lost too.

So, I was thinking of using a high or low side current sensing IC and a FET to sink current. And to use a processor to read the new sensor and convert it to the new resistance.
It's limited range, like 115 to 200 F or so. I would like to be able to lower the limit too as well even if it is rarely. I need about 90F minimum for proofing yeast. Something I don't do often.

I just haven't done any measurements or experiments to figure out what I need to do.

---OP---

The OP's problem may be similar.

For the OP:
1. Is the potentiometer 2 or 3 wires?
2. What is the open circuit voltage?
3. What is the short circuit current?
4. Is there a relationship between the angular position and the terminal voltage?
5. Minimum? Maximum?
6. What's available to power the interface circuit?

67K is an ODD value.

I appreciate the help here! Ok I'll try to answer the best I can.
1) potentiometer is a 2 wire slide type
2) Open circuit voltage is 3.5v
3) short circuit current is 17.8 ua
4) basically the pedal slides the potentiometer up and down
5) Pedal up = 3.26v, Pedal down = 3.47v
6) I will be using a 5v source for power

I believe it's an odd value as the manufacturer doesn't have to worry about it as any variance can be calibrated within the drum module itself. I believe this is so any other manufacturer's electronic hihat drum pedal could be used. I believe I can offset any non linear problems within the module also.
 
Picture this:

A single supply OP amp whose output drives an NPN transistor through a series resistor.
Emitter connects to (hopefully ground).
Collector goes to the TOP of where the POT was. This point also connects to (-) of the OP amp.
(+) of the OP amp then becomes your setpoint.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top