By Kathryn Rateliff Barr
Electrical engineers use breadboards to assemble one-of-a-kind demonstration circuits. A breadboard provides temporary connection points between the individual electronic components. Electronics professionals use breadboards because they can make changes in the circuits without complex work. This makes breadboards ideal for circuit development and testing. The temporary nature of the contacts limits most breadboards to low voltage, low power circuits. Using breadboards also limits the use of high frequency signals.
Most breadboards provide a grid of contacts where the spacing between contacts points is 1/10-inch square. This spacing matches the pins spacing of most integrated circuits and the pins of all transistor packages. This spacing facilitates connecting all the electronic components within the voltage, current, and frequency restrictions of common breadboards.
Number of Contacts
Breadboards provide a varying number of contacts. Depending on the manufacturer, a breadboard could contain as few as 75 or as many as 900 separate connection points. Manufacturers usually arrange the connection points in columns of 10 separated by a center median. This arrangement provides 56 connections for a standard 14-pin integrated circuit, four connections for each pin on the device.
Many breadboards are rated for five volts at one amp. A second common option provides a 15-volt, one-third amp rating. Both specifications yield a power dissipation of five watts. Check the manufacturer's data sheet for specific information prior to purchasing the breadboard since these specifications vary per vendor and device.
Most breadboards have a current limit of one amp or less, due to the nature of their contacts. Often breadboards can withstand only 1/3 amp.
Most breadboards cannot withstand frequencies above 10 MHz. The nature of the contacts inside the breadboard creates stray capacitance on the order of 2 to 20 pF for each connection. These capacitances are random, unpredictable and difficult to reproduce. Removing and reinserting a component lead sometimes appreciably changes the contact capacitance at that point. These effects become a considerable part of the circuit behavior above 10 MHz, making circuit analysis impossible.
Capacitance is defined as resistance to a changing current. Capacitance results from the action of two conductors separated by an insulator. When you insert a component lead into a breadboard, the connection is never perfect. The small imperfection results in a small capacitance at the connection. This equates to a 2 to 20 pF capacitor in series with each connection, where the current has no choice but to go in the correct direction.
The spring contact technology in most breadboards provides a convenient means of creating temporary electronic circuit connections. However, the same technology that makes breadboards useful creates comparatively large resistance at each connection. You can expect contact resistance on the order of 1/10 ohms per connection, while higher resistances are common. This can cause unexpected results in some circuits.
- Gary Barr; Concept Engineering; Garland, TX
- PSP: Datasheet: Solderless Breadboard (840 Tie Points) with Binding Posts
Rev. Kathryn Rateliff Barr has taught birth, parenting, vaccinations and alternative medicine classes since 1994. She is a pastoral family counselor and has parented birth, step, adopted and foster children. She holds bachelor's degrees in English and history from Centenary College of Louisiana. Studies include midwifery, naturopathy and other alternative therapies.