BCSEG PCB Ruler

The Ruler

Congratulations on discovering the Easter Egg hidden within the BCSEG PCB Ruler! This ruler isn’t just a practical desk accessory; it’s a tool designed to educate and inspire anyone interested in electronics.

What is the BCSEG PCB Ruler?

At first glance, the BCSEG PCB Ruler serves as a handy reference for anyone working in the electronics field. Here’s what it offers:

Electronic Symbols: A quick guide to common circuit symbols for easy reference.
Wire Gauge Diameters: Visual and dimensional guides for various wire sizes.
Component Pitch and Sizing: Helpful for identifying and measuring components.
Physical Ruler Scale: A functional ruler for measurements.

A Hidden Circuit Inside

But there’s more! Embedded within the ruler is a hidden working circuit. When assembled with the appropriate electronic components, this circuit transforms your ruler into a simple, portable flashlight.

This hands-on feature is a fantastic opportunity to practice soldering and learn more about assembling basic electronic circuits.

Note: Your PCB Ruler may be a different revision number — meaning it’ll contain minor differences in layout and/or appearance. However, it will function the same.

Circuit Diagram

The PCB Ruler contains a simple set of components that combine to form a simple circuit which lights an LED with the switch is pressed to make a flashlight.

When assembled into a circuit:

The battery provides 3V power to the circuit.
The switch controls the flow of electricity, turning the circuit on or off, when pressed.
The resistor limits the current to acceptable values to protect the LED.
The Light Emitting Diode (LED) creates the red light that you see.

Bill of Materials

To assemble the flashlight circuit, you will need the following:

[R1] 1Kohm Resistor Surface Mount (SMD)
- Example: Yageo, Part# RC1206FR-0710KL
[S1] Tactile Switch (SMD)
- Example: C&K Switches, Part# KMR211NGLFS
[D1] Red 5mm LED, Thru-hole (THT)
- Example: Wurth Electronics, Part# 151051RS11000
[XB1] Coin cell Battery Holder for CR1220 (SMD)
- Example: Keystone, Part# 3000
[B1] 3V Coin Cell Battery, Size CR1220
- Example: Duracell, Part #CR1220

You may have picked up the components when you received a Ruler. Alternatively, the components are available from common online sources or local electronics stores.

The components are available for order online from:

Tools and Equipment

The following tools are recommended:

Tweezers
Flush Cut Pliers
Soldering Iron
Solder (lead-free recommended)

If you don’t own these tools, we recommend asking family and friends to borrow. Use the opportunity to share the project with them and ask what they have learned from past soldering experience.

How-to Solder References:

If you haven’t soldered before here are some links covering the basics.

Note: Read, review, and follow all user manuals, instructions, and safety related recommendations from manufacturers when using these tools.

Assembly Instructions

We recommend following the instructions in the order provided. By soldering the components from thinnest to tallest, it keeps the ruler flat and easier to solder the next components in-place.

Locate the R1 resistor designator and footprint on the backside of the ruler.
Apply solder to one of the 2 pads of the resistor designator.
Place the 1K resistor in position and re-heat the solder on the single pad. Check that the resistor is flat to the surface of the board. Solder the second pads into place.
Note: The value indicator silkscreened on the top of the resistor is not required to be facing upwards to function, but it is best practice to ensure it is visible.
Flip the ruler over to the front side.
Locate the S1 component designator on the top side of the ruler, the side with our logo.
Apply solder to one of the pads.
Place the S1 switch component onto the pads. Orient it length wise to fit the footprint and re-heat the solder on the single pad to secure it in-place.
Solder the remaining 3 pads for the switch.
Flip the ruler over to the bottom side.
Locate the XB1 Coin Cell Holder designator and footprint.
Place the coin cell holder in place and solder in-place repeating the past process.
Note: The third centre pad will be hidden under the holder and does not require any solder (this is where the negative of the battery will press against the pad to complete the circuit).
Flip the PCB ruler over and locate the D1 component designator.
Slide the thru-hole LED component into the holes on the PCB. Ensure that the orientation is correct, the D shape of the LED component must align with the outline on the board.
Note: The polarity, or orientation, of this component is important or else it won’t work.
Flip the PCB ruler over while holding the LED tight to the surface.
Apply solder to the two leads of the thru-hole light emitting diode (LED).
Use the flush cutters to snip the LED leads as close to the board as practical.

Test The Ruler!

Insert the coin cell battery into the holder. Ensuring the proper polarity (positive side upwards, away from the surface of the PCB).

Push the switch on the top side and see your ruler light up!

Troubleshooting

If the LED is failing to light up, there may have been issues introduced during the assembly process.

Start by checking the orientation of your battery. The coin cell as a top and bottom and it is important it is oriented the proper way. Check the photo provided in the instructions above and confirm its placement.
If it still won’t light up, it is possible there is a “cold solder joint” (https://en.wikipedia.org/wiki/Soldering#Cold_joint). Go over each of your soldering connections with the iron one by one re-heating them to ensure the solder has flowed between the pad on the PCB ruler and the component pins.
Finally, check the polarity (orientation) of your LED. It is important that the direction is correct. Check that the flat (positive) side of the LED aligns with the silkscreen marking (D shape of the part) on the ruler.
If it still doesn’t light up. Using a multi-meter check that the coin cell battery voltage is greater than 2.1V. This minimum voltage is required to light up the LED. If it is, use the multi-meter to check each of the pad-to-pad connections throughout the circuit for continuity using the circuit diagram provided above as a reference.