On Thu, 24 Jan 2008 09:36:04 +0200 "Dumitru Stama" wrote: > Do i really have to have an opamp functional to test the voltages ? > I only have about 5v as VCC and it is a bit hard to supply the amp > with enough juice. I have already sent 0xFF to PORTD and i have > voltages close to VCC on every pin. I will try to build it again with > 100k and 200k resistors and check the voltages step by step, after > each part : 1bit, 2bits, ..... 8 bits. Depends _which_ circuit you have built. If it is the current-based one, you _need_ the opamp, as it must provide the virtual short circuit for the network to function. If it is the voltage circuit, you can test it _without_ the opamp, but be sure it is disconnected. Do check the last branch (where you connect the voltmeter, as this branch is different from the other ones. John -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist