Sorry all I was having a blonde moment All sorted now Chris Gavin-Egan wrote: > Sorry I may have confused things a little by mentioning the future plans > in terms of current display and temperature display. > > Please ignore that, as motor current is taken care of on different pins > and all that i was suggesting is that the display will show current > usage when the power is turned on and when the power is off the display > reverts to a temperature display. > > My only concern here is reading the analogue voltage input across those > two pins and getting a value from it. > > Chris > > peter green wrote: > >> it really depends on the level of the signals and the accuracy you need. the >> no hardware way would be to read both seperately through seperate ADC >> channels and subtract, if you wan't more accuracy or to save a pin on the >> pic then build a differential amplifier (one op-amp and some resistors) or >> an instrumentation amplifier (3 op-amps and more resistors but much higher >> imput impedance). >> >> >> >>> -----Original Message----- >>> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf >>> Of Chris Gavin-Egan >>> Sent: 24 September 2006 00:15 >>> To: Microcontroller discussion list - Public. >>> Subject: Re: [PIC] Relative Newbie needs assistance >>> >>> >>> 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 >>> >>> >> >> -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist