Convert Unipolar Squarewave to Bipolar Squarewave

[evolive]

Hello,

I'm looking for a chip that will allow me to take my hall-effect sensor's unipolar squarewave output and convert it to a bipolar squarewave.

The hall-effect outputs (digital!!!) only +V amplitude but I need to have -V and +V at the same time...

PLEASE PLEASE help me with finding a chip that does that or a circuit...

So far I heard that I can use capacitors... or an op-amp... with a dc-offset... but I am SURE there must be an IC out there that makes life easier. Thanks!

-sun

 

[Nigel Goodwin]

Hello,

I'm looking for a chip that will allow me to take my hall-effect sensor's unipolar squarewave output and convert it to a bipolar squarewave.

The hall-effect outputs only +V amplitude but I need to have -V and +V at the same time...

PLEASE PLEASE help me with finding a chip that does that or a circuit...

So far I heard that I can use capacitors... or an op-amp... with a dc-offset... but I am SURE there must be an IC out there that makes life easier. Thanks!

-sun

All it needs is a capacitor, this removes the DC offset.

 

[Sebi]

I mean, the easy way to use a MAX232 chip. It contain in-built charge pump supply, generate + and -10V from 5V. The RS232 side output swing from -10V to +10V.

 

[evolive]

All it needs is a capacitor, this removes the DC offset.

forgot to mention that the output of the sensor is digital... does that make a difference?

 

[evolive]

I mean, the easy way to use a MAX232 chip. It contain in-built charge pump supply, generate + and -10V from 5V. The RS232 side output swing from -10V to +10V.

i found a chip that someone recommended and its' the MC1488L... i haven't found out what exactly it is yet but i'll look into that max232

this won't effect the frequency does it? it's crucial as well. thanx!

-sun

 

[udi_hakim]

If you are having troubles with the 232 (though its a grate idea) You can also do it with any Opamp that feeds from a + and - power supply...

 

[Nigel Goodwin]

All it needs is a capacitor, this removes the DC offset.

forgot to mention that the output of the sensor is digital... does that make a difference?

No, it's an AC signal just the same, feeding through a simple capacitor will remove the DC offset, leaving the signal centered about ground.

What is it actually feeding into?.

 

[evolive]

It is feeding into a NTE995 Frequeny-to-Voltage Converter (equivalent to LM2917). It is used for a tachometer.

All it needs is a capacitor, this removes the DC offset.

forgot to mention that the output of the sensor is digital... does that make a difference?

No, it's an AC signal just the same, feeding through a simple capacitor will remove the DC offset, leaving the signal centered about ground.

What is it actually feeding into?.

 

[Nigel Goodwin]

It is feeding into a NTE995 Frequeny-to-Voltage Converter (equivalent to LM2917). It is used for a tachometer.

Have you tried it with the signal as it is?, it would be unusual for a single rail chip (which I presume this is?) to require an input centered around 0V.

 

[evolive]

I checked the signal of the he sensor and it was squarwave above 0.

I also used a function generator which had -V to +V and it worked. But as soon as I realized what the sensor was giving me... I tried offsetting the signal from the function genator above 0 so that it too will have only +V... and my tach stopped working. So my believe is just that... it needs -V and +V...

=\

My professor gave me a chip which is a MC1488L I have no idea what tha tis... so i'll get that done asap hopefully. As well as MAX232... wahtever that is... so far... the simplest one I've gotten is the OpAmp solution...

=| any more suggestion ideas? THANX!

-sun

It is feeding into a NTE995 Frequeny-to-Voltage Converter (equivalent to LM2917). It is used for a tachometer.

Have you tried it with the signal as it is?, it would be unusual for a single rail chip (which I presume this is?) to require an input centered around 0V.

 

[Nigel Goodwin]

My professor gave me a chip which is a MC1488L I have no idea what tha tis... so i'll get that done asap hopefully. As well as MAX232... wahtever that is... so far... the simplest one I've gotten is the OpAmp solution...

Considering I've suggested just a simple capacitor twice, I don't see how the simplest suggestion you've had is an opamp?.

From what I can remember, an MC1488L is an RS232 interface chip, but from your requirements that you have mentioned so far, you've never mentioned a requirement for that?. Is your actual requirement more than you've asked for?.

 

[Sebi]

I agree with Nigel, no need any signal conditioner.The comparator input can accept almost any signal. Just pull-up the input with 10k resistor (hall output is an open-collector) it will work.

 

[evolive]

I'll give the capacitor a try tommorow since i can't get into the lab to get my stuff out.

No special requirements really... it's just a simple tachometer that I want to work before competition

Sorry if I got you upset somehow...

thanx!

My professor gave me a chip which is a MC1488L I have no idea what tha tis... so i'll get that done asap hopefully. As well as MAX232... wahtever that is... so far... the simplest one I've gotten is the OpAmp solution...

Considering I've suggested just a simple capacitor twice, I don't see how the simplest suggestion you've had is an opamp?.

From what I can remember, an MC1488L is an RS232 interface chip, but from your requirements that you have mentioned so far, you've never mentioned a requirement for that?. Is your actual requirement more than you've asked for?.

 

[evolive]

hello,

what do you mean by pull-up the input with 10k resistor? and where would i connect the resistor to?

(you guys are all saying these things and im clueless... im not as good as you guys... (yet)

thanx!

I agree with Nigel, no need any signal conditioner.The comparator input can accept almost any signal. Just pull-up the input with 10k resistor (hall output is an open-collector) it will work.

 

[Sebi]

If You have a 14pin package, don't forget connect to GND the pin11. The pull-up resistor need between pin1 and positive supply, because the hall sensor output no give any signal without supply voltage (open collector).

 

[evolive]

i got it to work!

If You have a 14pin package, don't forget connect to GND the pin11. The pull-up resistor need between pin1 and positive supply, because the hall sensor output no give any signal without supply voltage (open collector).

your method probably works too since but i went the other way...

i read up on some comparator stuff... i'm thinking it's teh same as your method too xP

----------------

I tried teh capacitors and had only the polarized ones so I tried it anyhow... it worked but then it stopped... i guess it couldn't handle it?

Anyhow... I was going to get a bigger cap but no need for that now...

I'll post the final schematic for a working tachometer once i get it done...



Thank you for everyone who has helped me in this...

all i can say now is...

:thumbsup:

thanx!!!


ps. well... umm... the +comparator was bigger than the -comparator. -comp was going straight to ground and the +comparator didn't exactly go to 0 since it has to deal with the sensor (has some sort of resistance right?)... solution... use a resistor and a diode and give the -comparator .7V which for sure is larger than the +comparatoer hence it can switch on and off wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee