Digital oscilloscope project/kit

[John Rudd]

OFM.....what you been buying Rob?...

You should stop going on holiday...
I would have visited this w/e but you be out.....lol

Where you at your daughter's over the weekend ?
 
Rob

Yup, visiting yet again....the boys are growing bigger.... I think they'll turn out to be tuff geordies..lol...

[RobWilson]

True Geordies as well John 

Good to hear they are doing well  , maybe next time you're up mate   


Rob

[Bluechip]

Ok lads

A question for the electronics chaps ,   I would like to build a circuit that would charge up a bank of capacitors to anywhere between say  10v  to  35v and when charged  to the set voltage disconnect the power supply from the capacitor bank .   

Any pointers ?   


Rob

Nope, no Pointers, mates got a Staffy 

Depends on what you want to do, I'd use a PIC, one analogue channel to read a pot, and set the reqd. voltage and another to read the cap. bank volts.

Use one digital channel to drive a relay to disconnect when it's up to what you want.

How big is this cap. bank anyway ??  Not a good idea to try to charge a damn great heap of the things from zero without some attempt at a current limiter. A big cap. is close to a short circuit at initial switch on ... 
Stresses the rectifier no end ...

You going to Doncaster BTW ???

Dave

[RobWilson]

You going to Doncaster BTW ???

Dave

 

Hi Dave , whats on at Donny ?  will there be bacon or sausage  butties involved  ? 

Micro controlled , mmmmmmm sounds like a plan   

I was planning  to use a current limiting resistor to charge the caps .  As to the size of the cap bank thats still a big question mark  , I would like to build a small cap discharge spot welder 



Rob

[Bluechip]

Harrogate Show is at Doncaster this year, nowt to stop you taking your own bacon / sausage butties if you want. 

Or even a Hog Roast if you're that peckish ... 

Dave

[RobWilson]

  Hog roast would fit in the van Dave 

I will look into it , are you going mate ?


Rob

[Bluechip]

If you know the current the welder takes and for how long it takes it a first approximation would be:

Say ... 50A for 0.2 seconds ...

I x T = 1/2 ( C x V² )

So: Assume 50A for 0.2 seconds and an applied voltage of 35V

C = ( 2 ( I x T )) / V²

Which I make about 16 and a bit mF  or 16,500 uF

This does assume the cap. voltage stays at 35V all the time which it won't ... 

No real idea what current a spot welder takes or for how long?

Don't they have some sort of timer to gate the current ?? Another easy job for a PIC ... 

Dave

[Bluechip]

Hog roast would fit in the van Dave 

I will look into it , are you going mate ?


Rob

Yup, got my ticket   ... Codgers Discount rate ... 

Saturday probably ... about 90% certain.

D.

[Bluechip]

Have you got a diagram of what you want to build ... ?

Not having any real idea of how these things work, it seems to me to use a thyristor as the switching element as these turn off anyway when the current drops below the holding value and it wont switch on again until another gate pulse arrives ... 

D.

[PK]

Ok lads

A question for the electronics chaps ,   I would like to build a circuit that would charge up a bank of capacitors to anywhere between say  10v  to  35v and when charged  to the set voltage disconnect the power supply from the capacitor bank .   

Any pointers ?   


Rob

The details depend on things like how: how big the caps are, how fast you want to charge them, and what your input voltage to this circuit will be.

But essentially you would use a current limited power supply set to the target voltage and a diode. Very simple for small (ie <=10A) currents.
PK

[awemawson]

[/quote]


 

Hi Dave , whats on at Donny ?  will there be bacon or sausage  butties involved  ? 

Micro controlled , mmmmmmm sounds like a plan   

I was planning  to use a current limiting resistor to charge the caps .  As to the size of the cap bank thats still a big question mark  , I would like to build a small cap discharge spot welder 



Rob
[/quote]

Rob,

My stud welder has 200v caps of 66,000 microfarad, that charges up to a max of about 180 volt and will fix an M6 stud as per this thread (no pun intended !):

http://madmodder.net/index.php/topic,10358.0/all.html

[RobWilson]

Cheers for the input lads 


Looks like I will have to do some reading  up on capacitors , a classic case of Wilson running before he has even learned to crawl 


Canny stud welder Andrew  , good to read you got it all fixed . Used one myself many years ago    , I do remember one lads steel toecaps looking like two hedgehogs one morning
when he came into work   


Rob

[PK]

A simple constant current circuit is better than a resistor because it will allow faster charging.
I used this for a small anodising supply once.

[RobWilson]

That sounds a much better idea PK  , something I will look into .


Cheers Rob

[wheeltapper]

Hi
update on my non working airband receiver.
it's still not working.

I've checked all the elec caps, the're round the right way, all the chips are right way round in the correct places, I unsoldered one leg of each diode ( 4 in total ) and tested those, the're the right way.
the transistors are the right way according to the silkscreen.

I even pulled all the chips to check if I folded a leg over inserting them, all OK.

I'll try some voltage checks next.

Roy.

[John Rudd]

Roy, when you say its not working, can you elaborate a little please? Is there any audio?

Maybe theres no air traffic transmitting?

[wheeltapper]

sorry, I was a bit vague 

connecting the bnc socket to a long wire I have in the loft and touching the top of one of the chips with my finger I can barely hear a commercial radio station.

the 3 controls do nothing.

this is with a 9V battery, if I plug in a 12V wall wart the transistor mentioned previously gets hot even tho it's supposed to work on 12V.

there are a few voltages noted on the circuit diagram that came with it , one of them being 12V but there aren't as many as I would like.

I haven't had time to check them yet.

Roy.

[John Swift]

Hi Roy

the original project is here -

http://www.sentex.ca/~mec1995/circ/aviarx/aviarx.html


with 1K load resistors I don't expect the transistors to run hot
 but the TO-92 cased 78L08 regulator added to the Chinese circuit  could
 (depending the current taken by the receiver and the volt drop across the regulator)

   John


PS original circuit from http://www.sentex.ca/~mec1995/circ/aviarx/aviarx.html

[RobWilson]

  Thank you for taking the time to track down that build page John 

I am sure it will be a great help to me and Roy .

And the http://www.sentex.ca/~mec1995/circ/circuits.htm page looks full of interesting projects    

Rob

[John Rudd]

The voltage regulator serves no real purpose, there's insufficient headroom from a PP3 battery to allow the reg to function....
I'd be inclined to leave it out....

Just use a current limited power supply when testing the receiver for the first time....

[nrml]

I've just finished putting together my DSO138.


The SMT components were very easy to solder despite having absolutely zero previous experience with these. I used 0.25mm Pb/Sn solder, a pair of curved pointy tweezers and the largest chisel tip for the soldering iron that would fit on the little pads. No problems at all. In fact they were the easiest and tidiest part of the build. Some of the through hole components were a bit fiddly (the sliding switches especially) and the end product wasn't as tidy as the SMT bits but it all worked first time, so I can't really complain.

The acrylic case looks nice but there were a couple of problems. Firstly, the tabs for the sliding switches snapped the first time I toggled them and I had to remove them all. Secondly, one of the sides had slightly oversized tabs which snapped the plastic around the holes where it fits into.

Overall, it was a nice little project. Well worth the money. Now I  need to learn how to use an oscilloscope.

[RobWilson]

  looking very tidy nrml , Nice job 



Rob

[RobWilson]

Roy any joy with your Air band reviver ? 

Rob

[wheeltapper]

no, not yet.
I've checked everything I can think of, the circuit diagram that comes with it is no help, there are no voltages to check.

I know it's a spelling error when you called it a reviver but that's what it needs, reviving 

I've chucked it in the "to look at " box for now, it may end up in the "dump it " box. 

cheers

a disillusioned Roy.

[modeng200023]

I started a new posting about obtaining spares from jytech in Electronics and IC Programming.

John