Ferrite beads (L1 in the photo) filter high frequency power supply noise by converting it into a tiny amount of heat. Power supply noise can cause various problems for many parts, especially in analog audio and display circuits.

Ferrite beads are simple, but choosing one can be confusing because they’re not commonly used by hobbyists. Most designs will still work if you omit the ferrite bead(s), but beads are so cheap there’s no reason to sacrifice the added reliability they provide. We describe how we pick ferrite beads for our projects after the break.

A ferrite bead is rated for current, impedance, and resistance; see this Mouser listing for an example. Unless a datasheet or circuit requests specific bead characteristics, we choose a bead rated for sufficient current, and ignore the impedance and resistance values.

If the bead is for a power supply, we determine the maximum possible current the circuit will use and find a bead rated for double that amount. Last week we calculated the the Bus Pirate’s worst-case current consumption as 525ma, so we looked at beads rated for at least 1000ma. We used this one, which is rated for 1500ma and costs 10 cents.

Sometimes a ferrite bead is used to filter the power supply for one specific part of a circuit. We used a dedicated bead to filter the LCD bias voltage on the DIY digital picture frame, and with the ENC28J60′s ethernet transceiver on the web server on a business card. These parts only consume a few milliamps, so we used a smaller 200ma ferrite bead ($0.11).

Like this post? Check out the parts posts you may have missed. Want to request a part post? Please leave your suggestions in the comments.

DIP through-hole chips are an old package with instantly recognizable dual in-line pin rows.  Beginners love these chips because they’re large and look easy to solder; we abhor them because we hate messing around with the drill. Whatever your motivation for using a through-hole chip, use a socket whenever possible. A circuit board with socketed chips is easy to test without endangering the parts, and ICs can be removed, tested, and replaced, without resorting to a soldering iron. This week, by request, we looked at several common through-hole chip sockets.

DIP sockets are available in almost any pin-count, or you can use individual strips to make a custom size (Mouser #40-0518-10). ICs with less than 40 pins usually have .300″ row spacing, but many 40+ pin ICs are .600″ wide. Footprints are included in the Cadsoft Eagle default ic-package library as DILxx. Below is a list of our most commonly used DIP sockets.

8 pin .300″ socket (Mouser#571-1-390261-2, $0.14) This socket is useful for op-amps and small microcontrollers, like the 12F629 used in the Esquire e-paper cover.

14 pin .300″ socket (Mouser #571-1-390261-3, $0.15) Another small socket we occasionally need.

18 pin .300″ socket (Mouser #571-1-390261-5, $0.18) A very common chip size for lots of microcontrollers and 7400 series parts

28 pin .300″ socket (Mouser #571-1-390261-9, $0.30) Another common size for through-hole microcontrollers, and chips like the TLC5940 16 channel pulse-width modulator. Check your datasheet because a .600″ row spacing 28 pin DIP package also exists.

40 pin .600″ socket (Mouser #571-1-390262-5, $0.41) Watch out, this is a wide socket for chips with .600″ row spacing. Fits common 40 pin chips, like the PIC 18F4455 USB microcontroller.

Don’t forget to check out our previous parts posts.

Electronics parts can be a pain to choose. It’s often hard to tell from manufacturers’ datasheets if a part will fit your design. We auditioned six different tactile switches to find a cheap button to use in upcoming projects. A tactile switch, also called a momentary button or push-to-make switch, is commonly used for input and microcontroller resets. This type of button creates a temporary electrical connection when pressed.

Footprints for most of these buttons are available in the Cadsoft Eagle library switch-tac, or in the Sparkfun parts library under TAC_SWITCH. Buttons in the image above are discussed from left to right.

Through hole push button switch (6mm): This switch will appeal to fans of through-hole parts, but you can see that it’s actually smaller than the 6x6mm surface mount buttons. Note that it does not have the standard 0.1″ straight mounting legs, and thus won’t fit in a breadboard. Common package name(s): DTS-3 (S1 above).

642-MJTP1250 (16 cents)

Regular SMD tactile switches (6 X 6mm): A 6 x 6mm tactile switch is probably the most common surface mount button. Even though it’s surface mount, it’s large and easy to solder.  The button has two pairs of leads (1&2, 3&4) that connect internally to the same switch — although there are four legs you only get a single switch. You only need to connect one pin from each pair to use the button, but it makes no difference if you decide to connect both. The yellow and red buttons are rated in terms of the force required for activation (gf), yellow requires the most force (520gf) and makes the loudest snap. Common package name(s): DTS-6 (S2 above).

101-0164-EV (22 cents)

101-TS5922T5202-EV 520gf YELLOW (36 cents)

101-TS6824T2604-EV 260gf RED SMT (51 cents)

Small SMD tactile switches (4.5×4.5×0.4mm): Unlike the previous buttons, these tiny switches require practice and skill to solder. While the mounting area is only 12% smaller than the previous buttons, the leads are tiny and hidden under the package. Like the 6 x 6mm tactile switches, these are rated in terms of actuation force (gf). We were unable to find a ready-made footprint for this part.

688-SKRMAA 160gf (30 cents)

688-SKRMAB 260gf (30 cents)