Lewis Bates's Dissection Report for the Johnson Building Calculator

Introduction

Johnson Level & Tool was founded in 1947 with the sole goal of "Engineering Accurate, Durable, and easy to use tools that offer excellent value for the professional Tradesman." [8]

In addition to manufacturing this calculator, Johnson also produces laser distance measures, measuring wheels, digital measuring tools, digital levels, and protractors. [8]

The Johnson Building Calculator is a simple, yet durable calculator that is designed for use by professional tradesmen. It is a basic calculator that is designed to be used on construction sites,and in workshops.

The calculator is powered by a single CR2032 button battery and features a large, easy-to-read LCD display.

The calculator was designed to compute stair layouts including pitch, rise and run, as well as simplifying solutions for complete layouts, plans, bids, and estimates. [10]

It is perfect for stair layout including pitch, rise and run, as well as simplifying solutions for slope, arcs, and circles.[10] The calculator will also complete complicated rafter, square-up, circular, rake wall and board feet calculations. [10]

Product Market and Retail Info

Product History

Per Johnson's Website, there was little to be found about the product's history. [9]

MSRP and Street Prices

Per the Johnson Website, there is no MSRP. [9] The prices that can be found are listed below.

Retail Outlets

I bought the calculator at Lowe’s for $39.96. [11]

The only other retailer that I could find that sold the calculator was the Haus of Tools. [6]

They sell it for $55.99. [6]

Rebranded/OEM Versions

There were no re-branded versions to be found.

Operation

Keypad & Reset Button

The Calculator has a 40 key keypad arranged in an 8 x 5 format plus two switches for OFF and ON, that is 42 keys total.

There is a reset button in the upper left-hand corner. It can be activated when a small piece of metal such as the end of a paperclip is inserted into the hole.

LCD

The calculator Features a 1” x 2.75” LCD. It has the capacity to display a leading“1” out front with 7 whole numbers that display on 7-Segment displays.

The Display also has the capacity to show a decimal point at every 7-Segment. On the right hand side of the display, at the end of the segment of whole numbers, a two-digit proper fraction can be displayed in order to show fractional calculations.

A row of four 16-segment displays can be found below the row of Whole Numbers; This enables the calculator to use large letter abbreviations to display what mode the calculator is currently in.

To the right of the 16-segment displays, and Below the whole numbers, There are a series of hard coded words that exist to tell the user the unit of measurement that is currently being used: Ton, lb., SQ. Feet, In., cm., mm., etc. and to communicate whether or not a stored function is in use.

Finally, in the upper left-hand corner the display can render a singular “M” to show when data in temporary memory is in usage.

Human-Machine Interface

The Calculator is operated by the user turning it on when the keypad “ON” button is pressed, and turned off when the user presses the “OFF” button.

The user presses the keys and the input can be observed from the LCD Screen.

The user can also reset the calculator by either removing the battery or inserting the end of a metal paper clip into the reset hole.

Human-Machine Interface

Usage Timing Diagrams

Example Image 49

I measured the crystal of the calculator using the Rigol oscilloscope located in the upstairs of Brown Hall.

Here is a perfiect example of the 32.7kHz clock.

Product Analysis

When the Battery is inserted into the calculator, the LCD Illuminates with “RESET ALL”, waits and then illuminates a single 7-segment display, and waits for the user’s input.

From here, the user uses the keypad to input data into the calculator. These input values are stored into memory, calculated with other input values that are also in memory, and returns the Final, computed data into memory.

The final result is displayed on the LCD.

The calculator then waits for the user to either turn it off, in which case the screen is cleared and the memory is wiped, or for the user to input addition data that can needs to be computed.

High-level Product Design Diagram

High-level Product Design Diagram

Block Diagrams for Electronic Systems

The battery supplies power that is converted from chemical potential energy to electrical power, in the form of a digital signal, for the MCU to use.

The Digital signal is then read from memory and is then used to illuminate the LCD.

From here, the calculator waits until it senses user input from the keypad and then writes it into memory where it is stored.

Then, the data is read from memory and sent to the processor to be computed.

When the processor is finished computing the data, it is sent back to memory for storage.

Next, the data is read and sent to the LCD for display.

Now, the calculator waits for input from the keypad.

processor inputs and outputs

MCU

The battery supplies power to the Microcontroller unit (MCU).

From here, the MCU reads the default programmed settings into memory, and then sends them to the LCD in the form of serialized data.

The LCD then displays the values in the form of a “0” that illuminates the outline of a 7-segment display.

The input from the keypad is sensed from the peripherals and read into memory by the MCU.

From here, the MCU reads, computes, and sends out the data signal along with the data for the LCD to display.

When the reset pin is activated, it will restore all of the default settings into memory. Thus making the calculator anew.

Detailed Block Diagrams for MCU

Tables Showing Electronic Values

Tabular Electronic Values

I used the Energizer datasheet for the 2032 for these values. [4]

Complete Component-level Schematics

KiCad Schematic for the processor

This is the Schematic for the Processor and LCD side of the board.

KiCad Schematic for the keypad

This is the Schematic for the Keypad side of the board.

Complete Electrical BoM

Complete Electrical BoM

I used the Digi-Key link for calculating the cost of the crystal. [2,3]

I used the Digi-Key link for calculating the cost of the resistors. [14]

I used the Digi-Key link for calculating the cost of the capacitors. [15]

I used the STMicroelectronics link for calculating the cost of the MCU. [18]

I used the Digi-Key link for calculating the cost of the LCD. [19]

Complete Non-Electrical BoM

Tabular Electronic Values

I used the Amazon link for calculating the cost of the cardboard sheets that were used. [1]

I used the Grainger link for calculating the cost of the ABS plastic cases and covers. [5]

I used the Grainger link for calculating the cost of the silicone rubber keypad. [6]

I used the Home Depot link for the screws that held the battery terminals in place. [9]

I used the Small Parts link for the screws that hold the keyboard in place. [16]

I used the Small Parts link for the screws that held the outer casing together. [17]

Total Cost to produce the calculator

Total Cost

Reassembly

I removed the chip and burned the PCB of the original calculator, so reassembling the device was not possible.

Dissection Photo Journal

Photos and descriptions of each stage of the dissection process.

Example Image 1

Figure 1: The receipt of my purchase.

Example Image 2

Figure 2: The front of the unopened package.

Example Image 3

Figure 3: The back of the unopened package.

Example Image 4

Figure 4: The left side of the box.

Example Image 5

Figure 5: The right side of the box.

Example Image 6

Figure 6: The uncovered keypad and LCD of the Calculator.

Example Image 7

Figure 7: The protective cover of the Calculator.

Example Image 8

Figure 8: The inside of the protective cover and the back of the Calculator.

Example Image 9

Figure 9: The protective cover and the interface side.

Example Image 10

Figure 10: The CR2032 button battery in its packaging.

Example Image 11

Figure 11: Removed the first three screws on the back panel.

Here is the first look at the inside while it is still connected to the battery terminals.

Example Image 12

Figure 12: More of a close up of the last photo.

Example Image 13

Figure 13: shot of the unconnected terminals.

Example Image 14

Figure 14: The calculator now is fully disconnected from the back cover.

Example Image 15

Figure 15: Removing the 11 screws that hold the PCB, and keypad to the back of the front panel.

Example Image 16

Figure 16: the front side of the PCB with the keypad still in place.

Example Image 17

Figure 17: The major part of the dissection is now complete.

Example Image 18

Figure 18: Second one of the previous picture.

Example Image 19

Figure 19: Overhead of the PCB when I put it on the stand.

The LCD is disconnected from the PCB.

Example Image 20

Figure 20: back side of when it was on the stand.

Example Image 21

Figure 21: The largest chuck of epoxy that was removed from the top of the chip.

Example Image 22

Figure 22: The chip became detached from the mounting footprint on the PCB.

Example Image 23

Figure 23: Top side of the chip.

Example Image 24

Figure 24: The bottom side of the chip.

Example Image 25

Figure 25: Chip and PCB.

Example Image 26

Figure 26: scraped of the rest of the epoxy and accidentally burned the board.

Example Image 27

Figure 27: The detached LCD by itself.

Example Image 28

Figure 28: Glamour shot of the chip.

Example Image 29

Figure 29: My workstation that I used.

Example Image 30

Figure 30: Tools I used where 2 helping hands stands, two packs of stick notes for the BOMs, two phillips screwdrivers, a white extention cord, a pair of plliers and a cheap heat gun.

Example Image 31

Figure 31: I used a legal pad to sketch out the block diagrams of the calculator, before I finalized the diagrams in a pictoral diagram.

Example Image 32

Figure 32: I also used the pry bars from my electronics kit that is under the heat gun, and a electronic compact scale to weigh the resulting products.

Example Image 33

Figure 33: two foam blocks that hold the LCD in place.

Example Image 34

Figure 34: the same foam blocks.

I wanted to highlight the discrepacies in weight that can occur when using these types of instruments.

Example Image 35

Figure 35: The back cover.

Example Image 36

Figure 36: The clear plastic protector for the LCD.

Example Image 37

Figure 37: The paper packaging of the battery.

Example Image 38

Figure 38: The two screws for the battery terminals.

Example Image 39

Figure 39: The three black screws for the back cover.

Example Image 40

Figure 40: The eleven black screw that hold the keypad in place.

Example Image 41

Figure 41: The front plate.

Example Image 42

Figure 42: The protective case.

Example Image 43

Figure 43: The keypad.

Example Image 44

Figure 44: The epoxy.

Example Image 45

Figure 45: the cardboard box.

Example Image 46

Figure 46: Used a spotlight to identify the traces on the back side.

Example Image 47

Figure 47: Did the same for the keypad side.

Example Image 48

Figure 48: Highlighting the crystal on the PCB.

Example Image 53

Figure 53: The inner packaging.

Example Image 54

Figure 53: The Outer packaging.

Example Image 55

Figure 54: A differnt picture to highlight the traces from the processor.

Example Image 56

Figure 55: The LCD.

Example Image 57

Figure 56: The PCB itself.

Example Image 58

Figure 57: the black jumper cable.

Example Image 59

Figure 58: the red jumper cable.

I find it interesting that the Red weighs less than the black.

Footnotes

  1. Amazon. (n.d.). 50 Packs 9x12 Inch Cardboard Sheets, Premium Corrugated Cardboard Divider Inserts Bulk Flat for Shipping, Mailing, DIY Décor and Crafts. Retrieved November 9, 2024, from Amazon link
  2. ECS Inc. (n.d.). ECS-3X8 product page. Retrieved November 9, 2024, from Digi-Key link
  3. ECS Inc. (n.d.). ECS-3x8, 2x6, 1x5 datasheet. Retrieved November 9, 2024, from Datasheet link
  4. Energizer. (n.d.). CR2032 Lithium Coin Battery. Retrieved from Energizer link
  5. Grainger. (n.d.). Plastic pellets and colorants: ABS. Retrieved November 9, 2024, from
  6. Grainger. (n.d.). Plastic pellets and colorants: ABS. Retrieved November 9, 2024, from Grainger link
  7. Grainger. (n.d.). Silicone high-temperature rubber. Retrieved November 9, 2024, from Grainger link
  8. Haus of Tools. (n.d.). Johnson CALC-1500 Construction Master Calculator. Retrieved November 9, 2024, from Haus of Tools link
  9. Home Depot. (n.d.). M2-0.4 x 4 mm Grade A2-70 Metric Stainless Steel Phillips Drive Flat Head Machine Screws (10-Pack). Retrieved November 9, 2024, from Home Depot link
  10. Johnson Level & Tool Mfg Company. (n.d.). About Johnson Level. Retrieved November 9, 2024, from Johnson Level link
  11. Johnson Level & Tool Mfg Company. (n.d.). Building calculator. Retrieved November 9, 2024, from Calculator link
  12. Johnson Level & Tool Mfg Company. (n.d.). CALC-1500 instruction manual. Retrieved November 9, 2024, from Manual link
  13. Johnson Level & Tool Mfg Company. (n.d.). Johnson Level Building Calculator. Retrieved November 9, 2024, from Lowe’s link
  14. KOA Speer Electronics, Inc., “RK73B1FRTTBL103G - Thick Film Resistor, Anti-Sulfur, 10 kOhms,” Digi-Key Electronics. Accessed November 9, 2024, from Digi-Key link
  15. KYOCERA AVX, “LT05YD475MAT2X - 4.7 µF, 16 V, X5R MLCC, 0805 (2012 Metric),” Mouser Electronics. Accessed November 9, 2024, from Mouser link
  16. Small Parts. (n.d.). 18-8 Stainless Steel Machine Screw, Plain Finish, Flat Head, Phillips Drive, Meets DIN 965, 4mm Length, Fully Threaded, M3-0.5 Metric Coarse Threads (Pack of 100). Retrieved November 9, 2024, from Amazon link
  17. Small Parts. (n.d.). 18-8 Stainless Steel Machine Screw, Plain Finish, Flat Head, Phillips Drive, Meets DIN 965, 5mm Length, Fully Threaded, M3-0.5 Metric Coarse Threads (Pack of 100). Retrieved November 9, 2024, from Amazon link
  18. STMicroelectronics. (n.d.). STM32F030F4P6. Retrieved November 9, 2024, from STMicroelectronics link
  19. Varitronix. (n.d.). VI-301-DP-RC-S. Digi-Key Electronics. Retrieved November 15, 2024, from https://www.digikey.com/en/products/detail/varitronix/VI-301-DP-RC-S/531270