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
>
>
>
>
>   
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