Low Voltage Circuit

Speed Indicator For PCs Schematic Circuit Diagram

Overcoming CPU Speed Perception with a Circuit:

Speed indicator for PCs: For many, the principal attribute of a PC often boils down to its CPU clock speed, leading to the widespread tendency of judging a PC by the 2-digit speed readout. Machines registering below ’33’ (indicating 33 MHz) or lacking a display altogether are often dismissed from consideration. Essentially, if your PC doesn’t meet the speed expectations, you might find yourself out of the discussion. To address this ‘PC speed phobia’ and bring your PC back into the conversation, we present a circuit designed to simulate a significantly higher CPU speed than what is actually operating in the machine. With this, you can present an ‘old’ 12-MHz AT as having a ‘state-of-the-art CPU turbo speed of 66 MHz or even 99 MHz. After all, only you will be aware of the true clock speed ticking inside the unassuming grey desktop case.

Circuit Design and LED Segment Current Control:

Resistors R1-R14 play a crucial role in limiting the LED segment currents, and their values can be adjusted as needed (within reasonable limits) to modulate the read-out brightness. The activation of the ‘turbo’ speed indication is achieved through the switching action of transistor T2. Applying +5 V to the base of T2 results in T1 being switched off. Conversely, when the turbo switch is set to the ‘normal’ position, T2 turns off, and T1 turns on. This circuit playfully manipulates the perceived CPU speed to cater to those afflicted with ‘PC speed phobia’.

Unfortunately, there are differences between PCs as regards the logic levels used to switch between ‘normal’ and ‘turbo’ CPU speeds. In most cases, turbo speed is selected when the switch contact is a’make’ type that closes to ground. The table shown applies to that configuration. The table is also valid if the ‘normal’ position of the switch makes contact with +5 V; only R17 must then be removed. In the event that turbo speed is selected when the switch contact closes to +5 V, the table needs to be modified and R17 omitted. These modifications are also required, but R17 must be left in place if ‘normal’ speed is selected with the switch contacts closed to ground.

The modifications to the table are as follows:

(1) in the fourth (‘Normal’) column, change all entries *3 into *2

(2) In the fifth turbo column, change all 5s into 6s.

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Speed indicator for PCs The construction of the readout is simple on the printed circuit board shown (not available ready made). The board is cut into two to separate the jumper section from the display section. The two sections are interconnected by a 15-way SIL socket and a 15-way SIL header. Finally, note the wire ink that runs between the speed setting jumpers – if you forget to fit it. the displays will remain dark forever in the absence of heir supply voltage.

Speed indicator for PCSX
Speed indicator for PCs

Speed indicator for PC Parts list…

Resistors:
  • 14 270Ohme R1-R14
  • 3 3kohme9 R15; R16: R17
Semiconductors:
  • 2 BC337 T1; T2
  • 2 HD11050 LD1; LD2
Miscellaneous:
  • 14   2-way pin header
  • 14   3-way pin header
  • 1 15-way SIL socket
  • 1 15-way SIL header
  • 1 Changeover switch  (turbo switch in PC) S1
Speed indicator 55
Speed indicator for PCs
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