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HotKeys keyboard (2)

construction, software and a few tips

HotKeys keyboard (2)
Last month we described the features and the operation of this handy extra keyboard. Now it’s time to look at the hardware and the construction of the circuit.The schematic diagram of the hotkeys circuit is shown in Figure 6. All pins of the connector for the PC keyboard (K1) are connected through to the connector for the PC (K4), with the qualification that there is a pair of analogue switches inserted in the clock and data lines. These allow the hotkeys keyboard to open these lines. Power for the circuit is taken from K4. In addition, you can see a connector for the RS-232 interface (K2). Resistor R5 and diodes D1 and D2 limit the incoming signal to levels of approximately 0 V and +5 V.
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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,R2,R4 = 1k?
R3 = 330?
R5,R6,R10,R14,R18 = 10k?
R7,R15 = 2k?2
R8,R16 = 3k?9
R9,R17 = 6k?8
R11,R19 = 15k?
R12,R20 = 27k?
R13,R21 = 47k?
C1,C3 = 100nF
C2 = 10µF 16V radial
D1,D2 = BAT85
D3 = LED, red, high efficiency
D4 = LED, green, high efficiency
T1 = BC557
IC1 = MAX323CPA or MAX323EPA
IC2 = ST62T60 (programmed, order code 002006-41)
K1,K4 = 5-way SIL pinheader
K2 = 9-way sub-D socket (female), PCB mount
K3,K5 = 4-way SIL pinheader
S1-S16 = pushbutton, e.g. Marquardt (Conrad Electronic o/n 70 68 92-55, with cap 70 08 60-55)
Bz1 = 5-V piezo-ceramic buzzer (passive)
X1 = 8 MHz ceramic resonator
5-way DIN plug, pins arranged at 180 degrees
5-way DIN socket, receptacles arranged at 180 degrees
10 cm 5-way flatcable
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