Loading your content...

CFR12J 100R Resistor Guide - Specs, Uses & Circuit Tips | Communica South Africa

Overview: What is a CFR12J 100R Resistor?

CFR12J 100R resistors are general-purpose, carbon film resistors with a resistance value of 100 ohms (100R), widely used for signal limiting, biasing, current reduction, and pull-up/down in electronics. The 'CFR' denotes Carbon Film Resistor, '12' refers to the physical size/form factor (typically 1/4 watt or 0.25W), 'J' indicates a 5% tolerance, and '100R' specifies the resistance value. These resistors are cost-effective and well suited to a range of hobbyist, educational, and professional builds in South Africa, from breadboard circuits to PCBA production runs.

Technical Specifications

Parameter	CFR12J 100R	Typical Use
Resistance Value	100Ω	Current limiting, biasing, pull-up/down
Power Rating	0.25W (1/4W)	Low-to-medium power signals
Tolerance (J)	±5%	General electronics
Temperature Coefficient	±300ppm/°C (estimate)	Ambient operation
Body Size	~6.5 x 2.3 mm	Through-hole PCB, breadboard
Leaded/Lead-free	Usually RoHS compliant	Education, industry

Note: CFR12J 100R resistors are a staple in South African school kits, development boards, and industrial repairs due to their size, low cost, and ready stock at suppliers like Communica.

Common Applications in South Africa

LED current limiting in 3.3V/5V circuits
Microcontroller GPIO protection
Pull-up/pull-down on switches and logic lines
Input filtering (with capacitors)
Audio line loading/damping
Breadboard prototyping and lab exercises
Industrial panel repairs and quick fixes

Educational institutions often use CFR12J 100R resistors for coursework and design practicals. Local engineering repair shops also keep stocks for urgent service jobs, especially where rapid turnaround is essential and lead times from importers would delay repairs.

Key Selection Considerations

Power rating: Ensure the resistor can safely dissipate the expected power (see formulas below).
Tolerance: 5% is suitable for most circuits, but assess needs for precision.
Form factor: CFR12J suits breadboards, stripboard, and standard PCB holes. For SMD, look at 0805/1206 packages.
Availability: Buy in packs or bulk for educational or repair tasks; check Communica's stock status for branch collection or urgent orders.
Brand reliability: Brands such as Royal Ohm, UniOhm, and Yageo are commonly stocked at Communica, providing consistent quality in South African environments.

Calculations & Practical Examples

1. Basic Current Limiting (LED Example)

Using the CFR12J 100R resistor to limit current to an LED powered from a standard 5V logic rail:

LED forward voltage (Vf): 2.0V
Supply voltage (Vs): 5V
Resistor value (R): 100Ω
Current (I): (Vs - Vf) / R = (5V - 2V) / 100Ω = 0.03A (30mA)

Power dissipation in resistor: P = I2 x R = (0.03A)2 x 100Ω = 0.09W (well below the 0.25W rating).

2. Pull-down Resistor on Microcontroller Input

Connect one end of the 100R resistor to the input and the other to ground. This ensures a defined 'low' state when the switch is open, but resistance is lower than typical pull-downs (10kΩ is common), so check if higher current is acceptable.

Troubleshooting Tip: If the resistor gets hot to the touch, calculate power dissipation again, and consider a higher resistance value or a higher wattage variant.

Typical Wiring Diagram (ASCII)

    5V
     |
   [100R]
     |
    (LED)
     |
    GND

Troubleshooting Common Issues

Resistor is hot/burns out: Verify your power calculation, consider a higher wattage or resistance.
Circuit doesn't behave as expected: Double-check wiring, resistor color code (Brown-Black-Brown-Gold for 100R 5%), and continuity.
Lead times: For larger batches or class kits, contact Communica for bulk pack availability or to check branch stock before urgent jobs.

Local Notes: Availability & Sourcing

CFR12J 100R resistors are typically kept in stock at Communica's Samrand and Pretoria branches, with same-day pickup or rapid delivery across South Africa. Verify online for real-time stock levels, or call your nearest branch for time-sensitive projects. VAT invoicing is available for institutional and business customers.

Explore and Learn More

View the resistor category in Communica's online catalogue to find similar values for other standard circuits or to explore resistor packs for education and repairs. You can also explore trusted brands under Shop by Brand.

How to Use CFR12J 100R Resistors in Circuits: Practical Guide for South African Makers

Understand Key Specs

Circuit Application Tips

Buy Locally & Confidently

Communica South Africa

Overview: What is a CFR12J 100R Resistor?

Technical Specifications

Common Applications in South Africa

Key Selection Considerations

Calculations & Practical Examples

1. Basic Current Limiting (LED Example)

2. Pull-down Resistor on Microcontroller Input

Typical Wiring Diagram (ASCII)

Troubleshooting Common Issues

Local Notes: Availability & Sourcing

Explore and Learn More

Sources

DEC cc

Why Choose Communica?

*Free Shipping

7-Day Returns

Quick Delivery

Ian Mugede

Gerrard Cottrell

Erich Dixon

Quint Kloppers

DA Photography SA

Johan Grobler

Tobie Buckle

Raymond Phiri

Herman Beukes

Regardt Smit

Bonolo PowerMan

Kalvin Swart

Alfred Wolpe

John Airth

Walt du Toit

Gundo Ndou

Daniel Kloppers

Koos Liebenberg

THATO M

Deon Joubert

Jacques Westhuizen

Henriqui Dos Santos

Tokky Ademoyero

Julio Mondlate

Leon Ecroignard

Lennin Naidoo

Antoinette Myburgh

Paul Chien

Al

Trevor Sinyoro

Evan Jack

Hlompho Matobole

Jacob Mogano

Kevin

Omphulusa Nkwana

Ampsure Electrical (Ampsure Electrical)

Stephanie Yomi

AY Maleek

Phathwa Senene

Christian Motau

Marius van Niekerk

Tobie Wiese

Martin van Staden

Brenda Matete Maloma

Nolte Smit

Phillip Nthabalala

Simon Khasu

Dieter Claassen

Jax Panix

walter mangando

Chris Courtney-Stones

Mbuelo May

Carl De Beer

Willem Burger

Unarine Mulaudzi

Omega Shuro

Willie Biggs

Gary Kallis