using a Mosfet as a voltaje controlled resistor.

[eblc1388]

Horray Eric!!!
Your GIF is perfectly clear. I zoomed in to 2000% and it is still perfectly clear.

My black and white JPG is not perfectly clear but it is much better than a fuzzy colour one.

It only works one way, i.e. zoom up. One should try zoom down a GIF to 25% of the original and see what is the result.

I hated it when people posting 2000x1600 GIF schematic diagram which one must scroll to see all the circuit. Though the author often posted a "size reduced" version, its image quality is most of the time really bad.

If one tries "size reduction" of the original large GIF image using an image processing software, sometimes the end results are bad. The thin connection wires disappeared. In this case a jpg schematic might perform better, when printed out.

 

[ericgibbs]

Hi eblc.
I agree.

I hated it when people posting 2000x1600 GIF schematic diagram which one must scroll to see all the circuit. Though the author often posted a "size reduced" version, its image quality is most of the time really bad.

Hi Ron aka Roff,

Eric, what software are you using for schematic capture?

I was using an earlier version of screenhunter, BUT now I have used your screenhunter Ver5 link and it works just fine,,, thanks.

Hi agu,

Horray Eric!!!
Your GIF is perfectly clear. I zoomed in to 2000% and it is still perfectly clear.
My black and white JPG is not perfectly clear but it is much better than a fuzzy colour one.

Was this before or after your 'bedtime' drink...

 

[wombweller]

Thread off track or what?

What's the op?


Now this could have been a very useful thread of it's own and I'm surprised it wasn't suggested by the Moderator's who do like threads to be tidy as would be advised and expected.

I always save pic's as jpg. again in my ignorance on the matter.Now I will look at the alternatives so something as come of this thread.

I would have thought the way to go with this point would have been to say

"Eric you have given us a thought here with the some "fuzzy jpg's" lets make another separate discussion"

incidentally it would have been in my opinion better not to have directed the point at anyone in particular as this can feel like a good kick to the nut's especially when one is offering good advice.

This would have been useful thread to people like me who are very new to Electronics. I would ask that the point of putting images to the forum in the best possible method be started in a help thread.

BTW. Eric I am always pleased to see your jpg's slightly fuzzy or not.I have never given any amount fuzziness a thought.So long as it's enough for me to follow and re-draw in schema drawing software it's ok for me.

All you guy's are good for this forum (Eric,Nigel,audio) and I do like the input you have.I am very happy to have found such a forum and it is aiding me immensely with my new found hobby. Thanks to all who help!!!!!


BTW. what happened to the "edit" function I did like editing my posts at will!!

Sory Mortalo for confusing the thread even more, perhaps it better started again to keep it tidy. maybe the MOD's won't mind?


Mark

 

[Roff]

Hi eblc.
I agree.


Hi Ron aka Roff,

I was using an earlier version of screenhunter, BUT now I have used your screenhunter Ver5 link and it works just fine,,, thanks.

Hi agu,


Was this before or after your 'bedtime' drink...

Hi Eric,
Sorry, my question wasn't clear. I meant what software do you use to draw your schematics.

 

[ericgibbs]

Hi Eric,
Sorry, my question wasn't clear. I meant what software do you use to draw your schematics.

hi,
Gottcha,

I have Autosketch and expresssch [free], Lotus, Paint Shop Pro, old version of Sketch, Open Office and of course the MS add ons.

Prefer to use express as its quick and simple for small circuits.
One advantage with the expresssch is that its freeware, so any member can get a copy and I can attach drawings to emails

Did you have an alternative in mind, aways open to ideas.

 

[Roff]

hi,
Gottcha,

I have Autosketch and expresssch [free], Lotus, Paint Shop Pro, old version of Sketch, Open Office and of course the MS add ons.

Prefer to use express as its quick and simple for small circuits.
One advantage with the expresssch is that its freeware, so any member can get a copy and I can attach drawings to emails

Did you have an alternative in mind, aways open to ideas.

Well, I use Linear Technology's SwitcherCAD III (LTspice), and I think it makes very readable schematics. See below for a sample.

 

[ericgibbs]

Well, I use Linear Technology's SwitcherCAD III (LTspice), and I think it makes very readable schematics. See below for a sample.

Hi,
I do have that in my Program files and did browse thru it,but for some reason I set it aside, I will have a re-look.

Thanks,

 

[Roff]

Hi,
I do have that in my Program files and did browse thru it,but for some reason I set it aside, I will have a re-look.

Thanks,

It's primarily a simulator, but can be used just to draw schematics. The learning curve may be a little steep, but probably not too bad unless you also want to use it for simulation.

 

[ericgibbs]

It's primarily a simulator, but can be used just to draw schematics. The learning curve may be a little steep, but probably not too bad unless you also want to use it for simulation.

hi Ron,
I have 're-played' with LT, I recall the reason I side stepped it was, I could only save a diagram in asc format.
Drew a small circuit with a few components fairly simple.

Are you using the Screen grabber or a later/better version of LT than my one.?

 

[Roff]

hi Ron,
I have 're-played' with LT, I recall the reason I side stepped it was, I could only save a diagram in asc format.
Drew a small circuit with a few components fairly simple.

Are you using the Screen grabber or a later/better version of LT than my one.?

You can get free updates to LTspice, but I'll bet the version you have already will do what you need. It is a little clunky, but you can save a schematic by simply doing a copy (ctrl-C), or on the toolbar, go to Tools/Copy Bitmap to Clipboard. Then you paste it into MS Paint, manipulate it if you want, then save it as a PNG or GIF.

 

[ericgibbs]

You can get free updates to LTspice, but I'll bet the version you have already will do what you need. It is a little clunky, but you can save a schematic by simply doing a copy (ctrl-C), or on the toolbar, go to Tools/Copy Bitmap to Clipboard. Then you paste it into MS Paint, manipulate it if you want, then save it as a PNG or GIF.

hi,
When I ran the LT program it asked do you want to upgrade, yes.

Yes I follow, using PrnScn. ^C etc saving to clipboard as bmp, then converting to whatever.

The SH Ver5 does a good job, so for the present I'll go with that.

Many thanks for taking the time.

 

[Mortalo]

hi,
Assume you use a PMOS enhancement FET.
When the pot slider is at the top [on the drawing] the FET is not conducting so there is no voltage drop across the Rsense resistor.

If the pot is slowly turned so that the FET starts to conduct then the current thru the sense resistor will create a voltage drop across the Rsense.

This voltage drop will cause the current thru the Rsense and the FET to stablise. By choosing the value of Rsense and FET gate on voltage, values of 4mA thru 20mA can be achieved by adjusting the pot.

The Vsupply must be high enough to allow for the voltage drop across the Rsense, FET and Rload at 20mA.

A PNP transistor can be used in place of the FET.

For a Constant Current source, the gate voltage is derived from a fixed reference voltage. So as the load resistance varies the current in the load remains constant.

What are you using the current source for.?

sup eric !
looks like youre in trouble with the guys jejejejeje.

Well to tell you the truth. im using the mosfet stuff because i was told that i needed to design a system for temperature sensor at a distance of 1000 feet using the LM94022, using its whole range (-50C to 150C).

So i was sure i was doing it all right because....
this sensor when you have its pins (GS1, GS0 = 0) its output will be on a range of voltaje from 1.299v (for -50C) to 0.183v (for 150C) i know because theres a table in the datasheet that says so and i confirm it using a formula that the datasheet have.

so the voltajes for the gate that i calculated were...
vgs = 2.13 for 4ma and vgs = 2.6 for 4ma as i told you earlier, so i assumed that i needed to fix the span from the output of the sensor to the input of the mosfet.

So i used a voltaje divisor with 220 resistors at the output of the sensor and an opamp as a voltaje adder with a 2v ref so for example...

if the temperature were at -50C
Vk = 1.299/2 = 0.6495v
0.6495v + 2v = 2.6495
with this ID = 4ma aproximately

and if the temperature were at 150C
Vk = 0.183/2 = 0.0915v
0.0915v + 2v = 2.0915
with this ID = 20ma aproximately

so i guess that i could control the range of the temperature of the sensor if i had a control with the range of 4ma to 20ma and then sense that and convert it with a ADC of a 16F877A for example.

Ill put a diagram of the design.
so you can understand what im talking about.

 

[audioguru]

A lousy old 741 opamp won't work when its supply voltage is only 5V.
Its inputs won't work when they are within about 3V from a power supply voltage so the 2V input is too close to 0V and it will be dead. The other input also might be dead.

Each Mosfet is different and the circuit must be calibrated for each one, or negative feedback can make them operate almost the same.

 

[ericgibbs]

hi mortalo,

Is there any reason you cant use a standard 4 to 20mA driver ic.?
**broken link removed**

With sensor output from the
https://www.electro-tech-online.com/custompdfs/2008/06/LM94022.pdf

Is it the 1000ft cable run thats the problem.?

Dont use the 741, as stated, its not up to the job.

Look at the CA3140 OPA or similar, it will go close to zero with a light load, also allow a 3V overhead
above the maximum output swing required, on the +V power rail.

Dont worry about people having a go at me, I can take care of myself.
Seen it.....Done it.......Got the 'T' shirt.

I must say sorry to you, for myself and others to have misused your thread as a opportunity to have a go..

Regards