Re: gEDA-user: Design Lab Equipment

[Steven Michalske <smichalske@xxxxxxxxx>]

On Mar 31, 2007, at 7:43 PM, al davis wrote:

> On Saturday 31 March 2007 21:42, John Griessen wrote:
> > If you supplied a college purchasing dept with assembled
> > units, I imagine you'd get into ETL/UL testing for lab levels
> > of safety though.    Would University purchasing agents
> > reject kits?
>
> The purchasing dept has no clue.  It is up to the lab director.
> Sometimes the lab director is clueless.  Until you have
> experienced it, it is hard to comprehend what a problem that
> can be.
>
> UL approval is not really a problem.  Just use a UL approved
> wall-wart as a power supply.
We played with oscilator charging circuits for HV caps,  in lab we  
have more dangerous things than a curve tracer.....

> It probably makes more sense to just sell kits.  They can hire
> students to assemble them.
As a student I wanted to make one for an electronics class project,  
unfortunately I wanted mine to have computer control, and wasn't  
allowed to make that for the class.

It would be a great kit to have the students make as solder practice  
in their first electronics lab.  then they will have a tool that will  
be useful for time to come, why hire students to make them when it  
can be an assignment

A good design would be capable of testing both BJT and fets,  J-FET  
MOSFET MESFET, it would have been great to test the MESFET I fabed  
with a curve tracer I built.

Using a high power high voltage op-amp, like an OPA-541 or OPA-544  
both at 2 Amps, or a OPA-547 at 500mA as the output stage for the  
base drive would allow for large base currents.  For Vce an LM12 or a  
OPA549  to get the higher currents.  This could even be bolstered by  
adding an external Emitter follower BJT stage to give really high  
current drive :-)  maybe an IGBT might give even higher range :-)   
thus not requiring the really big op-amps.  just the design of a  
class AB output stage.

I guess coming up with concrete specifications would be a good idea.

30V 1A,
15V 100mA,
or 80V 15A

where do we want to go....  for students to test their 2N2222A  40V  
at 600mA surpasses to the current limit of the OPA-547.  I even  
remember taking small BJT's to failure to see what happens, in the  
classes curve tracer.  Often the lab tech at my school would have to  
replace drive components in the tracer as they would fail.

Having concrete device to study would be great,  this could be easily  
merged into classes too.  Amplifiers, current sensing techniques,  
perhaps isolation techniques to make really high voltage amplifier  
stages.


The other side of this coin is the software to control this device.   
How much intelligence does this device need.  Do we want a uC to  
control the operation,  I would.... but thats me.

Here is a simplified block diagram.

Attachment: curveTracer.sch
Description: Binary data

What do you guys think?

Steve


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