About the article


a 16-channel microcontroller-driven switching clock

The switching clock described here can control up to 16 channels and has 20 memories for individual switching times, each of which may apply to multiple days of the week. This clock has a very easy to operate, 4-button user interface. Monitoring of the outputs via an RS232 port is also possible. The ‘brains’ consist of an AT90S8515 from Atmel.There exists no shortage of switching clocks. Both ‘analogue’ and ‘digital’ (with LCD) models are available with widely varying features. So, what are the merits of this design that makes it deserve the light of day? Well, the particular feature that separates this clock from the masses, is that it does not control just one channel, but can be expanded to no fewer than 16 channels. In addition, this clock has a serial interface, which enables every on and off switching event for each channel to be monitored on a PC using, for example, HyperTerminal.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor 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.

R1,R2 = 3kOhm 3
R3,R4,R12,R13 = 1kOhm 5
R5-R8 = 2kOhm 2
R9 = 120Ohm
R10 = 220Ohm
R11 = 500Ohm preset H
R16 = 390Ohm
R17,R18 = 10kOhm
C1,C2 = 15pF
C3 = 18pF
C4-C9,C17 = 10µ F 25V radial
C10-C13,C16 = 100nF
C14 = 120nF
C15 = 150nF
D1,D2,D3 = 1N4148
D4 = LED, 3 mm, low current
D5,D6 = 1N4001
T1,T2,T3 = BC547B
IC1 = AT90S8515-8PC, programmed, order code 000184-41
IC2 = PCF8583P
IC3 = 24C02
IC4 = MAX232
IC5 = PCF8574P
IC6 = 7805
IC7 = TL7705CP
Bt1 = 3.6V NiCd battery with solder tags
X1 = 3.6864MHz quartz crystal
X2 = 32.768kHz quartz crystal
S1-S4 = pushbutton, 1 make contact, e.g., D6-0 (ITT/Schadow)
Re1 = 5V reed relay, DIL case, 1 make contact, e.g., Clare MSS21A05B
K1 = 6-way mini DIN socket, PCB mount
K2 = 9-way sub-D socket (female), angled pins, PCB mount
K3 = 14-way SIL pinheader for connecting LCD module
K4 = 2-way PCB terminal block, lead pitch 5mm
K5 = mains adapter socket, PCB mount
LCD module, 2x16 characters, e.g., Sharp type LM16A211
PCB, order code 000184-1 (see Readers Services page and website)
Disk, contains hex file and source-code: order code 000184-11
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