Shifting logic signals from 5v to 9v

[BigO]

I've been off & on working on a reverse engineering project of an old portable electronic device. The device is powered by a 9V battery. I think I've finally got enough of a clue about how it's supposed to be working that I'm ready to start trying to get it up and running.

 

The original integrated CPU/RAM/IO device operated at 9V. I want to emulate this device using a PIC or other low cost (and more importantly, available) uController. From studying schematics, it looks like downstream device (very, very, very obscure - no specs available) wants 9v on its inputs. I don't see 9v friendly microcontrollers popping up in any searches.

 

I'll test it using the 5v signals direct from the PIC, but I suspect I'll need to level shift the 5v outputs to 9v.

 

Anybody have any experience with a particular chip or method of doing this?

 

The signals are unidirectional, 8 bits, output from the PIC. Current sourcing requirements should be miniscule.

 

Thanks for any feedback or suggestions.

Edited August 2, 2009 by BigO

[GroovyBee]

For something quick and easy just use transistors and invert the signal sense in the PIC's software.

[+batari]

You can use something like a 4066 (quad analog switch) to drive logic at higher or lower levels. You will need two chips.

[BigO]

Thanks guys.

 

I was leaning toward the analog switch idea. I've used them in some of my designs before, but only on stuff that switched at practically static speeds. Of course, the original processor only ran at speeds in the kHz so it's not like it would be able to output signals at a scary fast rate.

 

The transistors are definitely an option. In the final solution (if I get that far), I'll probably go with the cheapest option.

[+poobah]

I wonder if you could use one of the max232 and friends with a couple zeners to knock the +12 down to do the trick.

[popmilo]

What about using some inverter, buffer ?

here is one:

CMOS Hex Inverting Buffer/Converter

CD4050B

 

http://focus.ti.com/docs/prod/folders/print/cd4049ub.html

 

If you would use VCC = 9V that would give you treshhold of 4.5 V

maybe just enough to be activated by pics 5V ?

and output would be 9V ?

[BigO]

What about using some inverter, buffer ?

here is one:

CMOS Hex Inverting Buffer/Converter

CD4050B

 

http://focus.ti.com/docs/prod/folders/print/cd4049ub.html

 

If you would use VCC = 9V that would give you treshhold of 4.5 V

maybe just enough to be activated by pics 5V ?

and output would be 9V ?

It's possible that any 9v friendly buffer, inverted or not, might work under those same conditions. I don't know how finicky they might be given operation relatively close to the threshold. However, I think I remember that a PIC can operate at 5.5 V so I might be able to cheat the output up to improve the reliability if the output level follows the supply voltage. Never tested that.

 

The same 4.5V threshold might apply to the downstream device in which case I'll have gotten lucky and can get away without explicit level shifting hardware. As if...

[BigO]

I can't believe I started this project well over 4 years ago...finally got to the point that I've proven the need to do the level shifting.

 

The CD4504B, with which I was previously unfamilar, is designed specifically for this purpose.

@ $.60ea/1, $.46ea/10, it's cheaper to use the chip than transistors and resistors.

 

http://www.mouser.com/ProductDetail/Texas-Instruments/CD4504BE/?qs=sGAEpiMZZMsty6Jaj0%252bBBmDx0n9pcbkk8BeHlEmrJRY%3d

Edited January 21, 2014 by BigO