Providing components and avoiding destructive circuits

How to open a local electronics laboratory for remote access

Part 4

Outline

Providing physical components for remote experimenters

Assuring that it is only possible to create 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

VISIR Laboratory - Providing components

As in the traditional laboratory the user is provided with a set of components needed for the experiment

These will be available on the breadboard in the lab client

The component set is prepared in advance by the teacher

Checking circuits

Before constructing the circuit in the switching matrix it is checked by the Virtual Instructor to ensure that it is safe

The Virtual Instructor is configured with descriptions of “safe circuits”

Laboratory Configuration

Experiments requires different components These requirements are often described in

the lab instruction manual Components to support the experiments are

mounted in the switching matrix Descriptions of “safe circuits” are provided to

the Virtual Instructor

From Circuit to Matrix

Virtual Instructor

Virtual Instructor

Circuit is wired on the virtual breadboard Circuit is checked by the Virtual Instructor If the circuit is safe it is allowed to be

constructed in the switching matrix

Cards in the Matrix

Osc. board

DMM board

Source board

Component board

Components used in lab exercises are installed in the matrix

Components for the

students

Breadboard

Matrix board

Node A

Node I

Node X1

Relay NR

Type, NR and Version

Matrix board

Socket for Multi-lead Components

Components Socket

Mounting a component

Component

Connection to Node A

Connection to Node B

Describing the component

All components that are mounted in the matrix are described in a component list

The resistor would be described as:R_2_7 A B 10k

Component Description

Type– R, L, C, OP, etc

Card and Relay Number– Refers to the exact position in the matrix

Nodes– Depending on the type the number of nodes can vary

Value– Component value, 10k, 10mH, 1uF, etc

Multiple relays

An excerpt from the Component List

OP_4_10:4_11:4_13  NC B D G NC C F NC   uA741

The OP component type has 8 connectors, of which pin 1,5 and 8 are not connected in this example. The component value is uA471.

Because of the many connectors several relays must be used to connect them all to the operational amplifier. All of them will close when the component is in use.

OP Pin Card Relay Description

2 4 10 4_10

3,4 4 11 4_11

6,7 4 12 4_12

Source board

Type, NR and Version

Relays to connect FGENA

Relays to connect Power

Source board functions

Connects the function generator to node A– Lower terminal hardwired to 0

VFGENA_24_1 A 0 Connects the channels of the power supply to

the bus– +/-25V is relative to COM– +6V is relative to 0

The source board usually has card number 24

Connecting the power supply

Extended nodes used:

Channel Bus node Relay

+6V X1 3

+25V X2 4

-25V X3 5

COM COM Hardwired

From bus to node

From the extended node, the power supply node can be wired to the node needed for the experiment, by using a jumper on a component board.

VDC+25V_24_4:4_5 F– The source board with card number 24, relay 4, will connect

the +25V channel to the X2 bus node.– A jumper has been installed on card 4, relay 5. Connecting

X2 to F.

The source connections are listed in the Component List

Excerpt from the Component List:* Power supply

VDC+6V_24_3 : 4_7        A VDC+25V_24_4:4_5 FVDC+25V_24_4:4_3    DVDC-25V_24_5:4_4    GVDCCOM_24_2        0

Channel Bus node Relay

+6V X1 3

+25V X2 4

-25V X3 5

COM COM Hardwired

Source board Component board

DMM Card

Low Side

High Side

Type, NR and Version

Oscilloscope Card

Channel 1

Channel 2

Type, NR and Version

DMM and Oscilloscope

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

OSC CH 1 OSC CH 2

FGEN CH 1

DMM

Power Supply

Example

Component listVDC-25V_24_5:4_4 GR_4_3 G H 220kR_4_2 H 0 120k

Avoiding destructive circuits

Provide the rules to the virtual instructor Safe circuits are described through Maxlists Contains a subset of the components in the

component list that can safely be used together

Can also describe source limitations Should also allow harmless wiring mistakes

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

VFGENA_1 A 0 max:5

VDC-20V_2 G vmax:-15 imax:0.5

R_R1 G H 220k

R_R2 H 0 120k

Max list

No relay instructions are needed

Measuring current

To allow for current measurement the DMM need to be connected in serial with the components in the circuit

This is made possible by replacing a jumper lead in the circuit with the DMM

May need to insert jumper lead in the circuit to allow current measurements in the correct places

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