Choosing proper interface chip - Electronic Circuits Projects Diagrams Free

vr · 16th June 2005, 07:44 PM

Hi,
Was wondering if someone here may be knowing of an interface chip, which can sit between a microcontroller and a sensor and do the level shifting per the following scenario:

Inputs pulses coming from a sensor (12v), need to be shifted down to 5v level by this chip, before feeding to microcontroller pins.
On the reverse, output from micro must be shifted up to 12v by the interace chip. This digital 12v level must appear on 8 pins on the interface chip, on the return path to the sensor.
(pulses will be 20 microsecond wide.)

Thank you.

**Jay.slovak** · 16th June 2005, 08:07 PM

Quote:

Originally Posted by vr

Hi,
Was wondering if someone here may be knowing of an interface chip, which can sit between a microcontroller and a sensor and do the level shifting per the following scenario:

Inputs pulses coming from a sensor (12v), need to be shifted down to 5v level by this chip, before feeding to microcontroller pins.
On the reverse, output from micro must be shifted up to 12v by the interace chip. This digital 12v level must appear on 8 pins on the interface chip, on the return path to the sensor.
(pulses will be 20 microsecond wide.)

Thank you.

I suppose one restor divider and one transistor+resisitor is enaugh, but you don't mention type of bus you use (serial/paralel).

**Nigel Goodwin** · 17th June 2005, 09:15 AM

Quote:

Originally Posted by Jay.slovak

I suppose one restor divider and one transistor+resisitor is enaugh, but you don't mention type of bus you use (serial/paralel).

Doesn't have to be a divider, a single resistor feeding a PIC pin is all you need (assuming you're using a PIC?), the internal protection diodes will clip the input to 5V, and the resistor limits the current they pass.

As suggested, for the output, a resistor from the PIC pin to the base of an NPN transistor, then a pull-up resistor from collector to 12V is all that's required - note that this will invert the polarity of the output, but this is easily compensated for in the software.

There are examples in the 'hardware extras' section of my tutorials.

It's not very clear exactly what you mean?, but if it's 8 bit parallel you will need eight of these!.

Agent 009 · 17th June 2005, 11:17 AM

if try with PNP, how to make it work?

**Jay.slovak** · 17th June 2005, 11:21 AM

Quote:

Originally Posted by Agent 009

if try with PNP, how to make it work?

I was thinking about it.. it won't work beacuse of differnet voltage levels.

Agent 009 · 17th June 2005, 11:35 AM

Yes, we need negative voltage for the base... But can't we do it?

**Jay.slovak** · 17th June 2005, 11:37 AM

Quote:

Originally Posted by Agent 009

Yes, we need negative voltage for the base... But can't we do it?

You can have the base negative against Emitor, but you can't make it positive or equal leveled!

**Jay.slovak** · 17th June 2005, 11:38 AM

If you use NPN to switch on the PNP (or use open colector pin on PIC), that would work.

Agent 009 · 17th June 2005, 11:40 AM

I think that's the best way, unless power and space r not problems, so just add inverters over all outputs, no???

**Nigel Goodwin** · 17th June 2005, 12:57 PM

Quote:

Originally Posted by Jay.slovak

If you use NPN to switch on the PNP (or use open colector pin on PIC), that would work.

Again, this is covered in the 'hardware extras' section of my PIC tutorials, but it's rather wasteful to add twice the number of transistors when a very simple software change saves half of them.

Agent 009 · 17th June 2005, 10:47 PM

Yeah, but maybe it's really strainful to change all the output of a very long program :? ...

**Jay.slovak** · 17th June 2005, 10:51 PM

Quote:

Originally Posted by Agent 009

Yeah, but maybe it's really strainful to change all the output of a very long program :? ...

As far as I know, every text editor has a Replace Function. If you search for BSF PortB,7 and replace it with BCF PortB,7 (and Vice versa) that would do the job...

(But it won't work with paralel or USART connection...) 8)

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16th June 2005, 07:44 PM	(permalink)
vr	Choosing proper interface chip Hi, Was wondering if someone here may be knowing of an interface chip, which can sit between a microcontroller and a sensor and do the level shifting per the following scenario: Inputs pulses coming from a sensor (12v), need to be shifted down to 5v level by this chip, before feeding to microcontroller pins. On the reverse, output from micro must be shifted up to 12v by the interace chip. This digital 12v level must appear on 8 pins on the interface chip, on the return path to the sensor. (pulses will be 20 microsecond wide.) Thank you.

17th June 2005, 11:17 AM	(permalink)
Agent 009	if try with PNP, how to make it work? __________________ May God be with you. My Blog

17th June 2005, 11:35 AM	(permalink)
Agent 009	Yes, we need negative voltage for the base... But can't we do it? __________________ May God be with you. My Blog

17th June 2005, 11:38 AM	(permalink)
Jay.slovak	If you use NPN to switch on the PNP (or use open colector pin on PIC), that would work. __________________ "I share, thus I am" Jay.slovak Read this! ICD2 Clone Best PIC/DsPIC Bootloader Read my Inchworm ICD2 review!

17th June 2005, 11:40 AM	(permalink)
Agent 009	I think that's the best way, unless power and space r not problems, so just add inverters over all outputs, no??? __________________ May God be with you. My Blog

17th June 2005, 10:47 PM	(permalink)
Agent 009	Yeah, but maybe it's really strainful to change all the output of a very long program :? ... __________________ May God be with you. My Blog