Providing components and avoiding destructive circuits

How to open a local electronics laboratory for remote access

Part 3

Outline

Providing physical components for remote experimenters

Assuring that it is only possible to activate harmless circuits

Advanced experiments Summary

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

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

Components used in lab exercises are installed in the matix

Components for the

students

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

The circuit is created in the matrix by wiring on the virtual breadboard

XML, TCP/IP, port 2324

Client computerside

EquipmentServer side

Virtual Breadboard Switching Matrix

The procedure creating the circuit in the matrix mimics how the student wires the circuit on the breadboard

Breadboard

Possible circuit node

Matrix board for components

23-04-18 ICBL 20089

A group of 6 wire holes forming a possible node

Node connector

20 pin IC socket for components with more than

two leads with wire holes

A component with two leads

Double pole relays

Single pole relays

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

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

An excerpt from the Component List

*This is comment Pin number

* Kort 4 1 2 3 4 5 6 7 8OP_4_10:4_11:4_13  NC B D G NC C F NC   uA741R_4_9        A B1.6kR_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.

Board number

These three components are installed on board 4

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

DMM, oscilloscope and sources connections

Source board

Osc. board

DMM board

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

The source connections are listed in the Component List

Excerpt from the Component List:* Power supply* Board 24 is the source boardVDC+25V_24_4:4_5 FVDC+25V_24_4:4_3    DVDC-25V_24_5:4_4    GVDC+6V_24_3:4_7        AVDCCOM_24_2        0

* Function generator

VFGENA_24_1 A

A0BCOMCX1DX2EX3FX4G

Circuit created if all installed components were connected

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

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

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

VFGENA_1     A 0 max:5VDC+25V_1    F    vmax:15 imax:0.5VDC-25V_2    G    vmax:-15 imax:0.5VDCCOM_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.

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

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

Example of simple a fixed circuit defined as a 16 pin IC

Connecting the fixed circuit on the breadboard to the matrix

Entering the circuit into the Component List

OP_2_8:2_9:2_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

Creating a Max List

VFGENA_1 A max:5

VDC+25V_1 F vmax:15 imax:0.5

VDC-25V_2 G vmax:-15 imax:0.5

VDCCOM_1 0

OP_2_8:2_9:2_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

Displaying the circuit and the extra components in the Component Box

A new option displaying the fixed circuit will be added

Part three summary

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