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Digital Caliper: Capacitive Scale and Slider with Two-Chip Electronics (Baxter and Buehler, Starrett, 1986)
A six-inch caliper that reads out on a display. Under the slide, a strip of etched copper bars runs along the beam. Electrodes on the slider pass a signal through the bars by capacitance, and the slider's electronics count the bars crossed and work out the position in between.
Result: a digital caliper reading in inches or millimetres, repeatable to a ten-thousandth of an inch, with floating zero, peak hold and high/low limits. It runs on two 1.5 V cells at 10-50 microamps.
Source: L. K. Baxter and R. J. Buehler (L. S. Starrett Co.), US Patent 4,586,260 (1986). Unknown: the metal of the beam, slide and rod, their dimensions, the processor's program, and how the chips and display are made. Ours: the etchant, photoresist and glue. Picture: Wikimedia Commons.
高级
2 days
说明
1
1
Etch the scale
Etch the scale
Etch the scale pattern onto a strip of copper-clad epoxy fibreglass with photoresist and etchant. Each copper bar is 0.40 inch long, with a wider centre 0.12 inch long and two ends 0.14 inch long. Space the bars on 0.05 inch centres: the centres sit 0.004 inch apart, the ends 0.025 inch apart. Run the pattern the full length of the scale. Ours: dry film resist and ferric chloride.
此步骤所需材料：
空白印制电路板（覆铜板）1 strip, length of the beam所需工具：
干膜光刻胶
氯化铁溶液
耐化学品手套2
2
Fix the scale into the beam
Fix the scale into the beam
The beam is a metal bar with the fixed outside and inside jaws at one end, a wide shallow channel in its face and a second channel along its back. Fix the scale permanently into the face channel, copper up. The patent allows etching before or after this step. Not given: the metal, the dimensions and how the scale is fixed. Ours: epoxy.
此步骤所需材料：
卡尺尺身1 with integral jaws
双组分环氧胶1 a little所需工具：
未知尺寸3
3
Fit the parts to the circuit
Fit the parts to the circuit
The circuit is one folded piece: a double-sided slider board joined by a flexible hinge to a circuit board. Its bottom face has two pickup electrodes, 0.750 x 0.110 inch and 0.0625 inch apart. On each side of them is an interdigitated transmitter array: fingers 0.115 inch long on 0.025 inch spacing, opening to 0.0375 inch at the centre. On the circuit board, solder or wire-bond the two chips: an NEC uPD7503 3 V processor (768 bits RAM, 2 kB ROM) and a CMOS gate array. Then fit the LCD, the 100 kHz crystal, the integrating capacitor and the MODE and SET buttons. Not given: the processor's program. Ours: a capacitor from a kit.
此步骤所需材料：
刚挠结合电路板1 slider board + circuit board
集成电路2 uPD7503 CPU, CMOS gate array
段码液晶屏1 5 digits
石英晶体1 100 kHz
电容套件1 one integrating capacitor
按钮2 MODE, SET
焊锡丝1 a little所需工具：
电烙铁4
4
Build the slide
Build the slide
The slide frame wraps the back and edges of the beam and carries the movable jaws. Fix it to the depth rod, which runs in the back channel of the beam; the rod's free end is the depth gauge. Put the moulded plastic housing between the frame ends. Fasten two metal wear strips under the slider board, one on each side of the scale. They ride on the beam and connect the board's copper to it. Not given: the metal and sizes.
此步骤所需材料：
卡尺尺框1 with jaws
未知金属1 depth rod and two wear strips
尺框外壳1 个所需工具：
未知尺寸
精密螺丝刀套装5
5
Assemble and check
Assemble and check
Fold the circuit into the housing recess, slider board facing the scale, and screw it to the frame. The electrodes must lie parallel to the scale bars at every point of travel. Put the two 1.5 V cells (the patent says 'zinc oxide') in the battery pockets of the circuit. The display shows five digits, a ten-thousandths bar graph, a minus sign and 'mm', plus PEAK, LOW, HIGH and LIMIT. Ours: check the reading against a vernier caliper.
此步骤所需材料：
机螺钉2 个
1.5伏纽扣电池2 个所需工具：
精密螺丝刀套装
游标卡尺材料
15- 1 strip, length of the beam占位符
- 1 with integral jaws占位符
- 1 a little占位符
- 1 slider board + circuit board占位符
- 2 uPD7503 CPU, CMOS gate array占位符
- 1 5 digits占位符
- 1 100 kHz占位符
- 1 one integrating capacitor占位符
- 占位符
- 1 a little占位符
- 1 with jaws占位符
- 1 depth rod and two wear strips占位符
- 1 个占位符
- 2 个占位符
- 2 个占位符
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