Providing components and avoiding destructive circuits

1
How to open a local electronics laboratory for
remote accessPart 3

• Providing components and avoiding destructive
  circuits

2
Outline

• Providing physical components for remote
  experimenters
• Assuring that it is only possible to activate
  harmless circuits
• Advanced experiments
• Summary

3
Component handling and circuit checking in a
local laboratory

• The instructor puts a set of components to be
  used in the lab session on each workbench
• During the session the students are permitted to
  activate the sources in their circuits only when
  the instructor have checked that the circuits are
  harmless

4
Component handling and circuit checking in the
VISIR laboratory

• The lab staff installs component sets for the lab
  sessions of a number of courses in the switching
  matrix
• A student can only use the set belonging to the
  lab session s/he has logged in to
• Checking if a desired circuit is harmless before
  it is activated is made by a virtual instructor
  using rules written by the teacher

5
Components used in lab exercises are installed in
the matix
Components for the students
6
Lab preparation in three steps

• The lab staff installs in the matrix the
  components listed in the bill of materials of the
  lab instruction manuals for the courses to be
  supported
• The teachers creates rules for the virtual
  instructor for each lab experiment
• The teachers care for that the proper component
  set are displayed in the component box on the top
  of the virtual breadboard

7
The circuit is created in the matrix by wiring on
the virtual breadboard
Virtual Breadboard
Switching Matrix
XML, TCP/IP, port 2324
Equipment Server side
Client computer side
The procedure creating the circuit in the matrix
mimics how the student wires the circuit on the
breadboard
8
Breadboard
Possible circuit node
9
Matrix board for components
20 pin IC socket for components with more than
two leads with wire holes
Node connector
A component with two leads
A group of 6 wire holes forming a possible node
Double pole relays
Single pole relays
10
Part of component board lay out

• The nodes are denoted A I and 0
• The other conductors in the node bus are denoted
  X1 X6 and COM. They are used for power supply
  connections and for future expansion

Relay number
11
Documentation of the matrix configuration
(Component List)

• All the components installed in the matrix are
  recorded in a list called Component List
  (component.list)
• The sources are recorded in the list too
• Component sets for several lab sessions can be
  online if the matrix has a number component
  boards
• The matrix driver, Circuit Builder, uses the
  component list to associate the nodes of an
  installed component to relay numbers

12
An excerpt from the Component List

• This is comment Pin number
• Kort 4 1 2 3 4 5 6 7
  8OP_4_104_114_13  NC B D G NC C F
  NC   uA741R_4_9        A B 1.6kR_4_8   
      B C 1.6k

The text in red is not a part of the list. It
only shows the pin order for components with
more than two leads. NC means not connected.
These three components are installed on board 4
Board number
13
DMM and oscilloscope connections possiblilites

• The DMM board has two inputs, one for voltage or
  resistance measurements an one for current
  measurements. Either of these inputs can be
  connected to any two of the nodes A I or 0 for
  floating measurements
• The ground terminal of both channels of the
  oscilloscope are hardwired to node 0. The other
  terminals can be connected to any of the nodes A
  I or 0

14
DMM, oscilloscope and sources connections
DMM board
Osc. board
Source board
15
Source connections possibilities

• The function generator can connect to node A. The
  low terminal is hardwired to node 0
• The dual floating power supply can connect to X2,
  X3. The common terminal is hardwired to COM
• The non floating power supply can connect to X1.
  The low terminal is hard wired to node 0
• The number of the source board is always 24

16
The source connections are listed in the
Component List

• Excerpt from the Component List Power supply
  Board 24 is the source boardVDC25V_24_44_5 FVD
  C25V_24_44_3    DVDC-25V_24_54_4   
  GVDC6V_24_34_7        AVDCCOM_24_2       
  0
• Function generator
• VFGENA_24_1 A

A 0 B COM C X1 D X2 E X3 F X4 G
17
Circuit created if all installed components were
connected
18
Teacher preparations

• All components required in a certain lab session
  must be online
• It must be possible to connect them so that the
  circuits in the lab assignments can be wired.
• It should also be possible to do harmless wiring
  mistakes

19
Means to avoid destructive circuits

• It is possible to set the maximum voltage or
  maximum current permitted to output from the
  sources
• The impedance levels in the loops permitted to
  create can be controlled

20
The teacher describes the rules in Max Lists
listing all connections permitted

• VFGENA_1     A 0 max5VDC25V_1    F   
  vmax15 imax0.5VDC-25V_2    G   
  vmax-15 imax0.5VDCCOM_1    0OP_1    nc1
  B D G nc5 C F nc8 uA741R_R1            A
  B 1kR_R2            A B 1.6kR_R3          
    A B 10kR_R4            B C
  1kR_R5            B C 1.6kR_R6          
    B C 10kR_R7            0 B
  1kR_R8            0 B 10kJUMPERLEAD_S1 A
  BJUMPERLEAD_S2 A DJUMPERLEAD_S3 B
  CJUMPERLEAD_S4 0 DJUMPERLEAD_S5 0 C

For example, omit the last line if the student
would not be allowed to short circuit the op.
amp. output.
21
A special virtual instructor rule for current
measurements using the DMM

• The DMM in current measurement mode are low
  impedance and must only replace a jumper lead

If you, for example, want to measure the short
cicuit current of the op. amp. this jumper lead
must be installed
22
Advanced usage

• The workbench can be used to probe a printed
  circuit board or other ready-made circuit with up
  to 10 test points
• It is also possible to include components from
  the component box and to use the power supplies
• The teacher preparations are the same. The fixed
  circuit can be displayed in the component box as
  an IC chip already available in the component
  library

23
Example of simple a fixed circuit defined as a 16
pin IC
24
Connecting the fixed circuit on the breadboard to
the matrix
25
Entering the circuit into the Component List

• OP_2_82_92_10 nc1 A nc3 nc4 G nc6 nc7 nc8 nc9 C
  nc11 nc12 F D B nc16 int1
• R_1_2 B C 1.6k
• R_2_2 B C 10k
• R_1_9 B C 1k
• R_2_11 B C 120k
• R_1_1 B C 4.02k

26
Creating a Max List

• VFGENA_1 A max5
• VDC25V_1 F vmax15 imax0.5
• VDC-25V_2 G vmax-15 imax0.5
• VDCCOM_1 0
• OP_2_82_92_10 nc1 A nc3 nc4 G nc6 nc7 nc8 nc9
  C nc11 nc12 F D B nc16 int1
• R_R1 B C 1.6k
• R_R2 B C 10k
• R_R3 B C 1k
• R_R4 B C 120k
• R_R5 B C 4.02k

27
Displaying the circuit and the extra components
in the Component Box
28
A new option displaying the fixed circuit will be
added
29
Part three summary
30
Summary part 1 - 3

• The VISIR laboratory is an enhancement of the
  local laboratory
• The software representing almost 20 man-years of
  work is published and you are invited to join the
  VISIR group and contribute to the further
  development
• The goal is producing engineers who have a solid
  and documented experience of laboratory work
  without increased cost per student for
  universities