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Digital Tachometer: Hand-Held Contact Type That Holds Its Reading (Sugiyama, Shimpo, US 4,000,465, 1976)
A hand-held digital tachometer. You press the contact head on its shaft against the end of a turning shaft and push the thumb button; a slotted disk inside chops a light beam into pulses, and the pulses counted in a fixed time, set by a quartz clock, appear in the window as the speed. A latch holds the reading after you take the tachometer away, so you can read it even where you could not see the window while measuring.
Result: a contact tachometer that shows revolutions per unit time and keeps the last reading.
Source: Y. Sugiyama (Shimpo Kogyo), US 4,000,465 (1976). Unknown: the number of holes, the clock, the gate time and the circuit details. Picture: the patent drawing.
Advanced
Unknown
Instructions
1
1
Make the housing and measuring shaft
Make the housing and measuring shaft
Make a cylindrical housing to hold in one hand, with a window in its side for the reading and a push button for the power switch where the thumb falls. Run a measuring shaft out of the front end in bearings and fit a contact head on its tip to press against the shaft being measured. Not given: materials, sizes. Ours: aluminium tube, a ball bearing.
Materials for this step:
Aluminium Tube1 housing
Unknown Metal1 measuring shaft
Ball Bearing1 piece
Unknown Material1 contact headTools needed:
Metal Lathe
Hand Drill
Unknown Dimensions2
2
Make the pulse generator
Make the pulse generator
Fix a disk on the measuring shaft with a ring of small holes evenly spaced near its edge. Put a light source on one side of the disk and a photodetector on the other: each hole passing makes one pulse. Shape and amplify the pulses. Not given: the number of holes. Ours: an LED and a photodiode.
Materials for this step:
Unknown Material1 slotted disk
LED Assortment1 light source
Photodiode (BPW34)1 photodetector
Resistor1 setTools needed:
Hand Drill3
3
Build the counting circuit
Build the counting circuit
Divide a quartz oscillator's clock down to gate pulses one unit of time long. Pass the measurement pulses through an AND gate during each gate pulse into a counter. At the start of each gate pulse a reset pulse clears the counter. After the gate pulse ends, the first measurement pulse that arrives triggers a latch pulse that loads the new count into the display. If the head has been taken off the shaft, no pulse arrives, no latch pulse is made, and the display keeps the last reading until the next measurement or until the power is switched off. Not given: the clock frequency and gate time. Ours: logic ICs and a seven-segment display.
Materials for this step:
Printed Circuit Board1 piece
Quartz Crystal1 piece
Logic IC Assortment1 divider, AND gate, counter, latch, reset
Seven-Segment Display Driver1 piece
Four-Digit Seven-Segment Display1 piece
Solder Wire1 as neededTools needed:
Soldering Iron4
4
Power it and measure
Power it and measure
Fit the battery and the thumb button as the power switch. Press the contact head against the end of the turning shaft so it turns with it, push the button, and read the revolutions in the window, now or after you take the tachometer away.
Materials for this step:
Battery1 piece
Push Button1 pieceTools needed:
Soldering IronMaterials
15- 1 housingPlaceholder
- 1 measuring shaftPlaceholder
- Placeholder
- 1 slotted diskPlaceholder
- 1 light sourcePlaceholder
- 1 photodetectorPlaceholder
- 1 setPlaceholder
- 1 piecePlaceholder
- 1 piecePlaceholder
- 1 divider, AND gate, counter, latch, resetPlaceholder
- 1 piecePlaceholder
- Placeholder
- 1 as neededPlaceholder
- 1 piecePlaceholder
- Placeholder
Tools Required
4- Placeholder
- Placeholder
- Placeholder
- 2 vendors sell this, none ship to you yetPlaceholder
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