About the article

Pico PLC

microcontroller or Programmable Logic Controller?

Pico PLC
There are certainly strong similarities between these two approaches to controlling equipment, and with the circuit described here we blur any remaining distinction still further. The Pico PLC employs only standard components and the necessary software development tools are available free on the Internet for private users.A distinction is frequently drawn between microcontrollers and PLCs (programmable logic controllers) used in industrial control applications. The first thing that is apparent is that the PLC is designed for industrial use: in particular this usually means a supply voltage of 24 V. Also, the circuit will be robust against supply polarity reversal, voltage spikes and short circuits.We find a further difference in the software. A PLC runs a monitor program which controls the sequence of events executed. This involves, among other things, the use of interrupts, software timers and dealing with various interface protocols (frequently RS-232 or CAN bus).
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Component list
R1-R8 = 1k?8
R9-R16 = 680?
R17,R36 = 4-way 4k?7 SIL array
R18-R25 = 10k?
R26 = 1k?
R27 = 7-way (or 8-way) 10k? SIL array
R28 = 3k?3
R29 = 330?
R30 = varistor 30V, 600mW, diameter 15-17 mm (e.g., BCComponents # 2322 5953006)
R31-R35 = 4k?7
R37 = 10k? (4k?7)*
C1,C3,C4,C7 = 100nF ceramic
C2 = 22pF
C5 = 47µF 16V radial
C6 = 47µF 35V radial
B1 = B80C1500 (80V piv, 1.5A), in round case
D1-D8,D17,D25-D29 = 1N4148
D9-D16,D20-D24 = LED. low current
D19 = 1N5407
IC1 = PIC16F84A-04/P
IC2 = 74LS151
IC3 = ULN2003
IC4 = 78L05AC
IC5-IC8 = LTV847 (Liteon), ILQ621 (Infineon) or PC847 (Sharp)
K1 = 10-way boxheader
K2-K9 = 3-way PCB terminal block, lead pitch 5mm
K10-K14 = 3-way PCB terminal block, lead pitch 7.5mm
K15 = 9-way pinheader
K16 = 6-way pinheader
RE1-RE5 = relay, 16 A/250 VAC (Finder # 40.61, coil 12VDC, 220?; or Omron # G2R-1-E 12VDC; or Schrack # RP310012)
PCB, order code 010059-1
Disk, test program, order code 010059-11 or Free Download
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