Author Topic: Digital oscilloscope project/kit  (Read 141305 times)

RobWilson

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Re: Digital oscilloscope project/kit
« Reply #175 on: January 10, 2016, 04:49:09 AM »
Hi Rob

just got back from the Everton v Manchester City match    (we won 2-1)

no I didn't build the LED scope
 I built a Vellerman LCD scope about 12 years ago
I've not used it for a while it needs the  6  AA nicads replacing

   John



Hi John

That looks a canny project , shame the kit is no longer available .


I dont do football  I prefer things with two wheels and an engine  :thumbup:  ,,,,,,,,,,,,,,the wife is a big Toon sports direct supporter   :lol:


Rob





RobWilson

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Re: Digital oscilloscope ,PSU,component tester and other electronics kits
« Reply #176 on: January 10, 2016, 05:02:10 AM »
While on the subject of PSU  , I bought the  0-30v PSU kit and it needs a mains transformer .

240v to 24v 

3 amp max

Would this one from ESR do the job   p#  311-312       https://www.esr.co.uk/electronics/products/frame_transformers.htm   

 



Cheers Rob

 

RobWilson

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Re: Digital oscilloscope project/kit
« Reply #177 on: January 10, 2016, 05:05:13 AM »
Yippee.
I think I've fixed it.
the first thing I did was reflow R18, that fixed the AC problem.

I just reflowed pins 1 to 7 on IC U2 and all the voltages are correct now.

PHEW!

thanks for the help.

Roy.


Good to hear you got it sorted Roy  :thumbup:


Rob

RobWilson

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Re: Digital oscilloscope project/kit
« Reply #178 on: January 10, 2016, 05:11:38 AM »
If the BG psu is the one Rob referred to, it has some flaws.....


John while searching the Banggood site I came across the PSU for the signal generator , a tad better than the suggested  one in the manual , I will still make the suggested one as I have the parts .

Anyway  http://www.banggood.com/DIY-USB-Boost-Single-Turn-Dual-Power-Module-Linear-Regulators-Multiple-Output-Power-Kit-p-1022517.html   , on order .

Input voltage: 5-24V DC
Output voltage: + 12V, -12V, + 5V, -5V , +3.3V.
Output current: 300mA (per channel)


Rob

Offline John Rudd

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Re: Digital oscilloscope project/kit
« Reply #179 on: January 10, 2016, 05:15:55 AM »
Rob,
There ara number of issues with that power supply kit, not least of all tha fact that a transformer with a 24 v ac secondary is going to give something like 36 v dc across C1...
Plus there is around 5v across D7.... This is totaling some 40 plus volts powering the three op amps...These are TLO81's with a maximum supply of 36 across their supply terminals....Result?  :zap:
Thecanswer to this problem is use op amps with a higher operating voltage or use a transformer with a lower secondary voltage....

To answer your transformer question, the voltage is too high, see the above....and the current rating too low to expect 3 amps from the power supply.....

If the shortcomings of the design are overcome, then a transformer with at least a va rating of 100 watts is needed....( dont forget the power supply is 'supposed ' to be good for 30 v x 3 A or 90 watts...realistically a 120 watt rated transformer is needed.....

If you want to run the power supply as designed, then go for a transformer with a lower secondary voltage.....but then that cant becallowed to go too low else the Negative voltage rail charge pump circuit wont give the designed voltage.....(C2,C3,R2 R3, D5/D6)
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RobWilson

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Re: Digital oscilloscope project/kit
« Reply #180 on: January 10, 2016, 05:40:45 AM »
My bad John

I copied wrong part number    :Doh:    , I meant this one   p#   312-612   12 - 0 - 12 3A 72VA Chassis Transformer   

So you reckon the op amps need upgrading , any recommendations mate . 

Rob
 

RobWilson

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Re: Digital oscilloscope project/kit
« Reply #181 on: January 10, 2016, 05:56:55 AM »
Anyway to small ,   why use VA ?    is VA just Watts ? 


volts  x amps .


Rob

Offline awemawson

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Re: Digital oscilloscope project/kit
« Reply #182 on: January 10, 2016, 06:11:21 AM »
VA is WATTS with the Power Factor taken into consideration. Power Factor relates to the way the phase of the voltage and current vary. Typical PF of a motor is 0.8


https://en.wikipedia.org/wiki/Power_factor

http://www.power-solutions.com/watts-va
Andrew Mawson
East Sussex

RobWilson

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Re: Digital oscilloscope project/kit
« Reply #183 on: January 10, 2016, 06:20:01 AM »
Hi Andrew


so if an electric motor was    240v x8A x 0.8 pf =  1536 VA or near enough 1.5Kva  ,  any idea what the power factor of a transformer would be ?  is that another can of worms lol


Rob 

Offline awemawson

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Re: Digital oscilloscope project/kit
« Reply #184 on: January 10, 2016, 08:16:52 AM »
Big transformers have PFs nearer to unity whereas little ones can be as low as 0.5 - it depends how much trouble they went to designing the magnetic circuit

http://www.the-power-factor-site.com/Transformer-Capacity.html
Andrew Mawson
East Sussex

Offline shipto

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Re: Digital oscilloscope project/kit
« Reply #185 on: January 10, 2016, 11:52:57 AM »
Mine lives  :ddb:
2 pics one with the self generated signal and the second with the signal generated by my other oscilloscope.
sen1 switch is a little temperamental it needs jiggling a little to work properly but I will live with that.
Turns out this life c**p is just one big distraction from death but a good one. For the love of god dont give yourself time to think.
https://myshedblog.wordpress.com/

Offline John Rudd

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Re: Digital oscilloscope project/kit
« Reply #186 on: January 10, 2016, 02:43:45 PM »
In answer to Rob's question on the 0-30 v power supply....

Any one cinsidering building this, my recommendation fwiw .......http://www.ti.com/lit/ds/symlink/opa445.pdf

These op amps have a better survival rate at 43v than the orig TLO81's originally specified.....
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RobWilson

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Re: Digital oscilloscope project/kit
« Reply #187 on: January 11, 2016, 02:32:31 PM »
Cheers John  :thumbup:  , I may  getting a few for the PSU kit .

Nice one Shipto  :clap: :clap: good to see another up and running , do you or has anyone else who has built one of these DSO have any thoughts on a case  ?


Cheers Rob

Offline John Swift

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Re: Digital oscilloscope project/kit
« Reply #188 on: January 11, 2016, 02:56:51 PM »

well I've a bag of bits for the scope ordered

not decided if I should mount the capacitors and wire ended resistors on the back of the board so the display will fit closer to the main PCB 

or  mount the switches on spacers of some kind to bring them up to the level of the display

    John

Offline kayzed1

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Re: Digital oscilloscope project/kit
« Reply #189 on: January 13, 2016, 03:51:03 PM »
Well mine got the last blob of weld today, i found a PU in the draw that did 2V-6v-9v and 12volts so i used that to do the tests..
All worked as it should :bugeye: fitted the LCD and fired it up....we have light and pictures :clap: THEN!!! the trace went off, the rest of the screen is still lit up and all symbols are present. So i followed the trouble shooting giude and came up with two voltage errors.. L1 should be Neg 8.11volts but ut is high at 11.57 volts.  TP25 should be neg 8.08volts but it to is high at 11.56volts.
i have checked all the resistors and all are in the correct places...any thoughts?
Lyn.

Offline John Rudd

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Re: Digital oscilloscope project/kit
« Reply #190 on: January 13, 2016, 04:10:01 PM »
Lyn,
I suspect the scope has suffered a death blow.....your wall wart thing must have too many ziggies coming out......

Things to check:

The voltage at TP 20 needs to be near that indicated on the schematic........

Check the voltages around TP21 and TP23....
Measure the voltages around Q1 and Q2...
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Offline John Swift

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Re: Digital oscilloscope project/kit
« Reply #191 on: January 13, 2016, 04:17:41 PM »
check the 3v3 at TP23  this is the reference at one end of R42 (1K)

the junction of R41 and R42 is the feedback voltage going to the V-MON input of U1

an error at V-MON =  TP13 =  pin 16 affects the actual voltage at TP25 the -8V supply

the actual voltages measured  depend on the positive supply at J 9 and J10

I'd expect the voltage on TP13 to be about +2V when the -8V switching supply circuit is working correctly
« Last Edit: January 13, 2016, 05:25:20 PM by John Swift »

Offline John Stevenson

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Re: Digital oscilloscope project/kit
« Reply #192 on: January 14, 2016, 01:56:49 PM »
Just got one of the transistor / components checkers delivered from China.
Bought the ready made up on as it was only a quid more than the kit ???

However no paperwork or instructions, anybody got a link to some somewhere ?
John Stevenson

Offline kayzed1

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Re: Digital oscilloscope project/kit
« Reply #193 on: January 14, 2016, 02:59:20 PM »
Many thanks all, i will have a play on Friday.
John S, PM me your address i got two sets of destructions in my pack i will stick them int post.
Lyn.


Ow! John R, does that mean ( the high volts ) that the scree will be an EX- screen now?

Offline John Rudd

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Re: Digital oscilloscope project/kit
« Reply #194 on: January 14, 2016, 03:33:59 PM »
Lyn,

Not the ex - parrott sketch.... :lol:

The extent of any overvolts damage cannot be determined without further checks and possible component replacement to resolve the existing problems...
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Offline Fergus OMore

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Re: Digital oscilloscope project/kit
« Reply #195 on: January 14, 2016, 03:48:07 PM »
For two quid at a fair some years back, I bought Telequipment Serviscope Minor that 'lights up' has wiggly green lines. Needs another probe( my limit of present skill) so can I get instructions that a near idiot could understand or should I dump it please?

Hopefully, I haven't pee'd on your parade.

Regards

Norman

Offline John Swift

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Re: Digital oscilloscope project/kit
« Reply #196 on: January 14, 2016, 04:49:09 PM »
after a quick web search - http://www.thevalvepage.com/testeq/telequip/servmin/servmin.htm

its a bit older than the scopes I was thinking of

found some service info
http://www.gd7rvp.co.uk/uploads/1/9/5/0/19504259/serviscope_minor.pdf

after looking at fleabay   I'd say don't dump it straight away
you could find someone  daft enough to pay a lot more money  than I expected

is this the info you are looking for ?
http://www.owlnet.rice.edu/~phys112/Lab/oscilloscope.pdf

    John
« Last Edit: January 14, 2016, 05:34:58 PM by John Swift »

Offline Fergus OMore

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Re: Digital oscilloscope project/kit
« Reply #197 on: January 14, 2016, 05:52:11 PM »
Gosh John, you are doing well, having been born in 1667!  Seriously, thank you for taking time to help me

Cheers

Norman

Offline John Swift

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Re: Digital oscilloscope project/kit
« Reply #198 on: January 14, 2016, 06:58:55 PM »
 
Hi Norman

no problem , I help when I can

I nearly was named Johnathan
I'm not that old, I'm only in my 60's but this last few weeks have felt a lot older

as a result of an old injury
I have sciatica from time to time  that make simple tasks like putting on socks a half hour ordeal
you have to keep moving and do what you can , when you can


RobWilson

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Re: Digital oscilloscope project/kit
« Reply #199 on: January 16, 2016, 10:57:44 AM »
Afternoon Lads


The next Bangood project  :zap: .................. A frequency counter and crystal tester  :dremel:

http://eu.banggood.com/Wholesale-Warehouse-1Hz-50MHz-Crystal-Oscillator-Five-LED-Display-Frequency-Meter-Kit-wp-Uk-959592.html


Its a half hour job to weld the components in , :dremel:




I tested it with a few crystals









Seams to work a charm  :thumbup:   


Cheers Rob