Week #15: (5/2-6) Interfacing, Driving Circuits.

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Week #15: (5/2-6) Interfacing, Driving Circuits.

Post by rjagodowski »

This week we will continue Last Week's Discussion on Hardware, Software, Diagnostics. with emphasis on Interfacing and Driving Circuits. The Incubator circuit schematic shown in last week's discussion includes both bipolar junction and a MOSFET devices to control loads with current and/or voltage requirements greater than can be supplied by the BS2 I/O ports directly. This will be one of the topics of discussion today.

Here are the schematics:
Fig. 6-17 Incubator Schematic Diagrams from Process Control Text.jpg
Fig. 6-17 Incubator Schematic Diagrams from Process Control Text.jpg (112.87 KiB) Viewed 363 times

For the Incubator circuits:

The 2N3904 is used to turn the heater ON/OFF:
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And the BS170 is used to turn the fan ON/OFF:
(1.57 MiB) Downloaded 37 times

There are many solid-state devices manufactured now which can support very high voltages (up to 1,000's of volts) and very high currents (1,000's of amps).

And of course, relays can also be used to drive higher voltage/current loads. Remember from the Syntax and Reference Manual that the output current of each I/O pin is limited, as is the Maximum I/O current available from a bank of 8 pins. It depends whether the outputs are sinking/sourcing, but these numbers generally range from 20/25 mA per I/O pin to 40/50 mA per IO Byte group.

Omron Relay Datasheet:
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And these are the relays being used in the EET-265 Advanced Automation Class:
(700.76 KiB) Downloaded 31 times
It's important to be able to determine the voltage/current requirements of each relay to determine what type of interfacing circuity is needed to drive it properly.

Other Parallax related hardware which can be used for interfacing:
(932.67 KiB) Downloaded 32 times
(2.19 MiB) Downloaded 27 times
The latter IO Board also supports the Sharp Solid-State Relay:
(239.75 KiB) Downloaded 32 times

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