EDIT:
Set Rout for 2.442V at 1Amp.
This will give [2.442/5]*1024 = 500 decimal [0x1F4] counts in the ADC regs, do a left shift to give 1000 decimal [0x3e8].
So from the sheet you posted I can assume the results are "good enough"
Sadly I still dont understand the above part you posted. I just don't get the conversion and how it takes care of the non-proportional nature of the results?
Also how does a left shift do what is required? For the last week or so I have been a little worse than usual in the concentration department, though they have not found any particular cause for my memory problems. But they have changed the tablets I take for it, maybe just for the fun of seeing what happens to me!
Would it be easier to explain the theory if I phoned you? I'm sure I have your number.
EDIT:
Al,
look at these values, I have shown 0 to 1000mA in one block and 0 to 100mA in the other block.
[the best resolution will be about 2mA, if you want a higher resolution you could use a 2.5V ref or amplify the Vout]
The ADC counts are shown in decimal, you will have to convert the ADC '10 Bit binary values to ASCII for displaying.
There are many binary to ascii convert subroutines
Eric
Edit2:
do you have the +V supply of the Max4172 connected OK to the input side of the 7805.???
Look at the Error plot on page #4 of the d/s,, less than 10mV Vsense, its awful!
The 7805 Vin is about 8.5v so thats enough but I thought of another potential problem. Would the contacts of the switch possibly have a resistance that could mess up the readings? I know many switches and relays boast a contact resistance of a few mOhms but that may be enough to screw up the readings?
Also I have been researching the way I was planning on limiting the current, using a 317T in current mode and for the life of me I can't find out if it needs a headroom voltage like it does in Vreg mode?
If it does need some headroom then I would have to put it before the 7805 and then I would also read any current used by that as well as the load.
This project is getting way more complicated than I envisaged! I only started it as a good way to use one of my recently acquired large 16x2 LCD displays!
Doh! thats the old brainbox malfunctioning again! Of course it measures after the 7805!
As to the negative supply. Yes it does, I was planning on just measuring the actual voltage of this to display along side the positive variable side. I sometimes use the pos and neg rails without the GND to get the 30v that is needed to test various things like LED backlights from laptop screens which tend to have 8 or 9 LEDs in series, its quite handy for that, but since I don't do a lot with amplifiers and such I don't use it for what I presume is its original purpose.
Did you have something in mind that involves the negative rail?
hi Al,
I am looking at the 5V current sense using an OPA and a 2N3819 [ which I believe you have?] or do you prefer to stick with the max4172.
The sense circuit is working simulation, but I will try it in hardware.
Do you still plan to use a 317T for the current limiter.?
As you are using a CT transformer with a full wave bridge for the +V and -V outputs they cannot be isolated, you can still connect across +V and -V for a higher SINGLE voltage.
E.
EDIT:
I see that you have a 15v, 0, 15v. 1A CT transformer, I guess you know you will not get +15Vout or -15Vout at full current load due to diode drops and the overhead voltage required for the LM317.
I don't mind using other bits at all. I am happy as long as the job works.
I do have some 2N3819s but they are A's does this matter? I also have quite a few different op amps.
As to the transformer, I wrote the values that I actually measured at the outputs. Before the regs there is 18.5v on the variables and 8.5 on the 5v line.
Anyhow, just got to take my grandson home now, its the first time we've seen him for over a month due to his mum being awkward.
I have assumed a 15v,0,15v CT, transformer, rated at 500mA.
The Vout for testing was set at +12V and the current limiter for 500mA.
The current limit resistors for the limit selection will be: I lim = 1.25v/Rlim
The highest current with 12Vout is approx 350mA, after that ripple is high on the output.
I will run some tests later, with current circuit attached.
Eric
Added:
Shows the +5Vreg with limiting and simple current measurement voltage circuit.
Regarding getting 5v. The winding seems to be giving 8.5v to the 7805 so it has 3.5v headroom.
The other 3 connections are 18v before the lm317t's that controls the output voltage for each rail. So that side too has headroom.
One thing I have noticed though is that ONLY the variable side goes through a rectifier! The 5v side just goes to a large 4700u cap and straight on to a 7805. Weird that it has no rectification!
Edit: Just found the rectifier hidden under the transformer, obvious now I have stripped the unit!
I will try and do a circuit diagram but I am hopeless at drawing as you will have noticed. I wonder if I can find the diagram on the net? Nope!
Just a bit of extra info on the current available.
I am now certain that the 5v has 1A available but the variable rails share 500mA between them 250mA pos and a further 250mA for the neg side. I assume this means that even when using both rails without the center ground it will only give 250Ma?
Just a bit of extra info on the current available.
I am now certain that the 5v has 1A available but the variable rails share 500mA between them 250mA pos and a further 250mA for the neg side. I assume this means that even when using both rails without the center ground it will only give 250Ma?
Sorry to take so long to get back, had some more grandson problems.
I have gone cross eyed and allsorts trying to do a schematic of my PSU. Tried a couple of ways of doing one on the PC and failed dismally so decided just to draw it and scan it.
I hope it is good enough and that I have got all of it right. Even though it is single sided I had problems seeing all the routes as the component side is mainly heatsinks and transformer.
I have further measured the transformers outputs and at no load the +5 is actually 8v only dropping to 7.2 at a full 1A load.
The variable voltages are 23v at the input to the regulators and still maintain 18.5 at full load, thats roughly the same for both pos and neg sides.
Hope this is suitable to get some good ideas and a working ADC/ IADC.
BTW the other thread I started about writing to LCDs got way beyond me and two people I respect and who have both given me advice in the past got into a rather heated discussion about methods and I was frightened to reply in case either thought I was taking sides. The truth is that both were way above my knowledge level. I just didn't want two really helpful and respected members to argue because of something I started. Both Mike and Roman have been helpful to me in the past and I feel a bit guilty about starting the thread.
Anyway below is the scan, done by my good wife Dawn for me, as I don't have a scanner now and she has taken over the computer guru role!
EDIT: Would there be any problem in permanantly joining the grounds from both? I have done it temporarily in the past to try things but I wondered if there is any detriment to this. Can you foresee any situation where they would NEED to be separate? I am thinking that to measure the variable voltages I would need to join the grounds if I use the 5v side to power the ICs?