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 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 R_2_7AB10k Type Card Nr Relay Nr Node Value

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 One component may need many relays – As is the case with components with more than two leads Described by using sequence of card and relay numbers separated by : (colon sign) – X_1_1:1_2:1_3

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 PinCardRelayDescription 24104_10 3,44114_11 6,74124_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: ChannelBus nodeRelay +6VX13 +25VX24 -25VX35 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_5F – 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_5F VDC+25V_24_4:4_3 D VDC-25V_24_5:4_4 G VDCCOM_24_2 0 ChannelBus nodeRelay +6VX13 +25VX24 -25VX35 COM Hardwired Source boardComponent 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 list VDC-25V_24_5:4_4 G R_4_3 G H 220k R_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_10nc1 A nc3 nc4 G nc6 nc7 nc8 nc9 C nc11 nc12 F D B nc16 int1 R_1_2B C1.6k R_2_2B C10k R_1_9B C 1k R_2_11B C 120k R_1_1B C 4.02k

Creating a Max List VFGENA_1 A max:5 VDC+25V_1 Fvmax:15 imax:0.5 VDC-25V_2 Gvmax:-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 nc16int1 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 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