transistor issue - Page 1
Forum section: electronics / projects

author: @rt
author_rank: Super Contributor
timestamp: September 05, 2015, 10:51:17 am
content: Hi GuysThis has to do with my core rope project. Pulling my hair out here :OI send a pulse through the pulse line, and try to read the transformer outputsfrom the secondaries into an eight bit port. Only the first four bits are shown here.It is only bit 0 that is behaving itself.The input to the transistors from the former secondaries all look the same to me on a scope.This circuit should invert the signal, and usually be high, except when there’s a pulse.Bit 0 does this, but all others in the line are always zero volts (the highlighted connections) unless I pull the micro controller out of the circuit.I would think that the ten turn windings on the toroids would normally bekeeping the transistor bases low. The 5 Volt supply to all transistors is ok.Right now, this will read 0001, when it should be 0101 due to the pulse wire weave pattern shown here.Then as I cycle all the other pulse lines that aren’t shown here, the 8 bit result is either 0 or 1,and it is always bit 0 state, and is correct.Any ideas of what I should try? Thanks

author: Andy Watson
author_rank: Super Contributor
timestamp: September 05, 2015, 11:09:07 am
content: How big is the voltage pulse from the ten-turns sense winding? You're going to need at least 600mV before the transistors react.

author: @rt
author_rank: Super Contributor
timestamp: September 05, 2015, 11:17:17 am
content: Hi, yes they are all the same, but that’s irrelevant.Let’s say the pulse was zero volts. Then all the outputs should be high all the time.Only bit0 is normally high. The others go high when I pull out the micro, and drop down slowly to zero again.

author: Andy Watson
author_rank: Super Contributor
timestamp: September 05, 2015, 11:23:34 am
content: Ah, sorry, misinterpreted the problem.Is the power supply to the micro clean?

author: @rt
author_rank: Super Contributor
timestamp: September 05, 2015, 11:28:42 am
content: It is a 5V 2A regulated supply for Sony PSP, but I have also tried another supply.I’m about to disconnect the first secondary to see if that makes bit1 the new bit0.

author: @rt
author_rank: Super Contributor
timestamp: September 05, 2015, 11:56:00 am
content: The transistors can be forgotten about (except the unusual behaviour I think has something to do with it.I just removed the first two and connected the micro inputs directly to their former secondaries.It works the same.. only bit0 works, it’s just not inverted anymore.

author: Andy Watson
author_rank: Super Contributor
timestamp: September 05, 2015, 12:23:13 pm
content: If you measure the voltages - with micro connected - are the static (DC) conditions correct?

author: @rt
author_rank: Super Contributor
timestamp: September 05, 2015, 01:03:42 pm
content: All looks good around the micro. with a DMM, the transistorised pins that are left, the highlighted points are slightly below zero normally (-0.09V).If I measure the former output with a DMM that’s always going to look like a DC short to ground, and does.On a scope, the signal is above 600mV on all of them, but I can’t see the positive pulse once I connect something to it(either the mcu pin or transistor base).

author: atferrari
author_rank: Frequent Contributor
timestamp: September 05, 2015, 08:16:46 pm
content: Cores acting like ferrite beads but huge ones?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 06, 2015, 12:03:56 am
content: Sounds like you forgot to set the MCU pins to input (tristate or pullup drive)?Tim

author: @rt
author_rank: Super Contributor
timestamp: September 06, 2015, 03:18:45 am
content: First suggestion was correctSilly me wrote 0x01h to the port tris instead of 0FFh to set the eight bits input.That perfectly explains the first bit working as input, and the project is working nowThanks for the suggestions