Voltage is relative. It will run on +0 and -5 just as well as it will=20 on +5 and 0, or on +24 and +19, for that matter. Of course, the input=20 voltage needs to be between Vcc and Vee (or Vdd and Vss) But you already have an inverter available in your ADM222, so all you=20 need to do is cut off the +5V of the output with a diode. Kerry alan smith wrote: > OK one thing that I am not sure about is the tiny logic parts say they op= erate from 2 to 6 V...so your saying it can run at -5V just fine? > > > > ----- Original Message ----- > From: Dwayne Reid > To: Microcontroller discussion list - Public. > Cc:=20 > Sent: Tuesday, November 8, 2011 5:03 PM > Subject: Re: [EE] -5V to 0V swing from a +5 input (again) > > Hi there, Alan. > > I've been reading the various replies and thought that I'd offer my sugge= stion. > > First, though, I want to make sure that I understand the question. > > You have a signal that currently swings from 0V to +5V and you need=20 > to shift that to swing between -5V to 0V. > > Is the logic inverting? That is: when the input is +5V, the output=20 > should be -5V and when the input is 0V, the output should be 0V. > > Or should it be reversed? That is: when the input is at 0V, the=20 > output should be at -5V and when the input is at +5V, the output=20 > should be at 0V > > I assume that you already have both +5V and -5V rails available. > > My suggestion, for what its worth, would be either of two chips. > > 1) 4053 triple SPDT switch. Gnd pin =3D0V, Vee pin =3D-5V, Vdd pin =3D=20 > +5V. Feed the control input into the switch control line, tie the=20 > switch NO pin to whatever logic level you want, tie the switch NC pin=20 > to whatever logic level you want, take your output signal from the=20 > switch armature. You get 3 identical switches in the package - you=20 > can parallel the three sections for lower RdsON. Note that you can=20 > make this either inverting or non-inverting simply by swapping the NO=20 > and NC pins of the switch. > > 2) Tiny Logic gate such as Fairchild NC7S14M5 (dual, cascaded=20 > inverter with Schmitt Trigger input in SOT-23-5 package. In this=20 > case, you would connect the chip's Vss pin to -5V, the chip's Vdd pin=20 > to 0V, feed your logic input into a 5V zener diode (C to +5 input, A=20 > to junction of 2k2 pull-down resistor to -5V and one side of another=20 > 2k2 resistor, other side of the 2nd 2k2 resistor goes to input of the=20 > NC7S14 logic gate. You have your choice of logic inversion simply by=20 > choosing which output pin you use (inverting or non-inverting). > > Both of these are simple and inexpensive. The 4053 solution is the=20 > easiest because there are no extra components other than the=20 > chip. Do make sure that you get a CD4053 or equivalent - you do NOT=20 > want the 74hc4053 version because it is rated to only 6V rather than=20 > the 15V/18V (depending upon manufacturer) rating that the 4xxx family=20 > has. The cd4053 chip is available in several packages, including DIP and= SOIC. > > dwayne > > > At 06:58 AM 10/31/2011, alan smith wrote: > =20 >> hello...this goes back to a question I asked a few weeks=20 >> ago. Basically it was asking about generating a -5V signal from a +5V i= nput. >> >> So I settled on a ADM222, old style RS232 driver and sure enough I=20 >> can get the -8V drive. But what I need is -5V so thinking....on the=20 >> charge pump -V pin, putting a zener to clamp the voltage to=20 >> -5V....or....feeding that -V pin with a regulated -5V, wondering if=20 >> that might work. >> >> However the other problem is, when the input is positive, the output=20 >> goes positive, and I need that to be at the reference 0V level. I=20 >> tried to use a pull down to ground on the +V charge pump, but that=20 >> just pulled it from +8V to +5V. I'm not an analog oriented person=20 >> so...wondering if there is some sort of opamp based design that can=20 >> only allow the negative swing to go thru, and if its ever positive,=20 >> keep it at the ground reference. What happens if you ground the=20 >> positive rail on an opamp and just provide negative power? >> =20 > > > =20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .