OK one thing that I am not sure about is the tiny logic parts say they oper= ate 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 suggest= ion. 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?=A0 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?=A0 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.=A0 Gnd pin =3D0V, Vee pin =3D-5V, Vdd pin =3D=20 +5V.=A0 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.=A0 You get 3 identical switches in the package - you=20 can parallel the three sections for lower RdsON.=A0 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.=A0 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.=A0 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.=A0 The 4053 solution is the=20 easiest because there are no extra components other than the=20 chip.=A0 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.=A0 The cd4053 chip is available in several packages, including DIP and= SOIC. dwayne At 06:58 AM 10/31/2011, alan smith wrote: >hello...this goes back to a question I asked a few weeks=20 >ago.=A0 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.=A0 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.=A0 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.=A0 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.=A0 What happens if you ground the=20 >positive rail on an opamp and just provide negative power? --=20 Dwayne Reid=A0 Trinity Electronics Systems Ltd=A0 =A0 Edmonton, AB, CANADA (780) 489-3199 voice=A0 =A0 =A0 =A0 =A0 (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .