Ok guess Jpgs aren't allowed... here's a link to the jpg http://www.gavin-egan.com/thermistor.jpg The full diagrams can be found at www.sinclairc5.com Chris Gavin-Egan wrote: > My ascii drawing didn't turn out too well, here's a jpg > > > > picture of circuit to ula > > Chris Gavin-Egan wrote: > >> Hi all >> >> I've been lurking for a while and I have been working on a hobby project >> for the past year (when i have had time) essentially learning whatever i >> can when I have spare time. >> >> Working on projects like this are the only way i find that i REALLY >> learn, however I think i am now truly stuck and quite possibly out of my >> depth and that is one of those thing i hate admitting. >> >> Basically I am working on producing a daughter board with a 16f628-A pic >> on it to replace an ageing 21 year old Ferranti ULA chip that is >> pre-programmed for working in an instrumentation pod of a Sinclair C5 >> electric car. The problems associated with this is that I am working to >> the constraints of the original electronics that are there. I understand >> what the inputs and outputs of this chip are (which helps!!!) >> >> I am going to sell these to Sinclair enthusiasts when I finish, only >> because when the original chip malfunctions the C5 cant be driven. I >> will never make a profit with them because of the time and effort taken >> so far but in reality that is not the reason I am working on them. It is >> primarily just a project that forces me to learn but also because so >> many people over the years have made promises that they are working on a >> replacement chip for it and none have ever come to anything I dont want >> this project to fail and I am so close. >> >> The choice of 16f628 was primarily because of the I/O count ADC and the >> size of the chip in comparison to the ULA which is a 28pin DIL (Giving >> me a little room for manoeuvring within the original chip outline) >> >> I am about 60% of the way there. My daughter board works in a basic >> fashion - it operates the power control to the main power relay- >> illuminates LED's as appropriate and and i am just now trying to get >> some of the other functions to work. >> >> The First problem i have is really as follows. >> There is a 5v supply feeding a thermistor that is as shown below which >> detects the temperature of the motor across a std voltage divider . >> >> >> 5v------- 10k ntc thermistor------------------------- ferranti dil >> socket input 1 >> | | >> | | >> | 100ohm >> 10nf | >> | | >> 0v-----------1k ohm------------------------------------------ferranti >> dil socket input 2 >> >> It has a thermistor and voltage divider on 2 pins of the chip and what i >> am having problems with is understanding how to get pic to accept the >> voltage across these two pins. >> >> The operation of the system is that when the 10k thermistor reaches >> around 1000 ohms (in practice this is actually 750ohm )the input across >> the two is about 0.3 - 0.5v and the chip sets off an audible alarm i >> know it probably has a simple answer but my brain is now in a rut. >> >> What I was going to do is take the analogue voltage and display that on >> the LED bargraph as an approximate temp display. This display is >> presently being utilised by the ULA as a current meter for the motor, I >> simply thought that this display could be utilised as a temp display >> whenever the motor is not being used as well as utilising the audible >> output that is presently there. >> I hope this makes some sense. >> >> Its also funny how looking at this and talking about it on email has >> made me come up a couple of thoughts but my head hurts. >> >> Thankyou >> >> >> >> >> >> -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist