Shift Register Is All It Takes To Make A 3-wire Serial LCD

April 7, 2011 by Mike Szczys 11 Comments

This hack is a bit older, but one aspect of the setup makes it worth sharing. Shift registers are a common component to include in a project when you need to increase the number of I/O pins available. We’ve used them to drive LCD screens before, but we never realize you could use a 595 chip to make a 3-wire serial LCD interface. That’s because we’ve always thought of shift registers as having three control pins which must be addressed: data, clock, and latch. But it seems that’s not the case. This hack gangs the pins for clock and latch (called the storage register clock input on this chip) together. This causes the shifted data to be latched to output register one clock cycle after it is shifted into the chip.

This means you can operate the 595 chip with just two pins, but alas, you do need one more connection to drive the LCD properly. This is an HD44780 compliant display. It is being used in 4-bit mode; four of the shift register pins provide that data, while a fifth controls the Register Select pin. Since the shifted data from the 595 appears on the pins after each clock strobe, you must control the Enable pin on the LCD separately or it will behave sporadically.

So there you have it, control an HD44780 display with just 3-pins by using a $0.42 part. Are we going a little too fast for you? Check out this 595 tutorial and give the shift register simulator a try. That should bring you up to speed.

[Thanks Rajendra]

Circuit Building With A Hammer And Nails

April 6, 2011 by Mike Nathan 34 Comments

real_breadboarding

[Collin Cunningham] over at Make recently wrapped up another edition of “Collin’s Lab” – this time around, the subject is breadboards. He starts off by discussing a common solderless breadboard, something you are no doubt familiar with. What you might not know however is how breadboards got their name.

Way back when, before there was a RadioShack in every strip mall across the country, fancy prototyping supplies like your solderless breadboard did not exist. Amateur radio operators would prototype circuits on wooden boards, often using whatever was around as a substrate. Many times, this meant that the family’s cutting board ended up as a makeshift prototyping station.

One popular method of building circuits was to drive small nails into the breadboard, using wire wrapping to connect things together. [Collin] demonstrates this technique in the video, constructing a simple LED flasher circuit.

He says that the process works decently enough, and was kind of fun to do. He does mention however that building any sort of circuit requiring an IC would likely be out of the question.

If you have a few minutes to spare, check out the video embedded below – [Collin’s] take on technology is quirky and entertaining as always.

Continue reading “Circuit Building With A Hammer And Nails” →

Everything You Need To Know About Wall Warts

April 6, 2011 by Kevin Dady 25 Comments

If you work with electronics at any skill level you need juice. [Jon] has a great, and clearly worded tutorial about Wall Wart Power Supplies with pretty much everything you need to know about those little black boxes hanging off of your outlets.

The whole thing starts off with the basics like transformers, rectification smoothing and regulation, then moves on to the different basic types, dedicating a page to linear, regulated and switching types, giving output performance charts under different situations.

Also included is a run-down of DC barrel jack structure so you get the right plug every time, wall wart type identification, a random sample comparison test, and a good selection of formulas to even keep the old hats reading along. Although you might want to set aside a little time at 9 pages and some Q/A in the comments, it might take a moment to read.

Hacking Automated Hand Sanitizers With Ben Heck

April 5, 2011 by Mike Nathan 9 Comments

benheck_sanitizer

If you have visited a hospital any time recently, you probably noticed quite a few automated hand sanitizer dispensers scattered throughout the hallways and in each patient’s room. Since hospital-acquired infections are a growing problem, there has been a push for all personnel to use these hand sanitizers regularly to lessen the likelihood of spreading disease.

In the most recent episode of his web show, [Ben Heck] took on the challenge of hacking one of these dispensers to use motion sensors in order to sense when hospital personnel are near, as well as to remind them that they should sanitize their hands on the way out.

He disassembled the dispenser to see how it operated, then worked on replacing the IR sensor pair with a set of motion detectors. He hooked the motion sensors to a Propeller board, which uses a separate add-on board for keeping time. Once the motion sensors are triggered, the passer-by is given a window of time before the machine notifies them to kindly sanitize their hands. All movements and sanitizer dispensing events are logged to an SD card connected to the controller, which can be reviewed to ensure policy compliance.

If you have about 20 minutes to spare it’s worth checking out, and if you are interested in more hand washing tech, check out this DIY hand dryer we featured a while back.

Kapton Tape Aids In Drag Soldering Surface Mount Parts

April 3, 2011 by Mike Szczys 29 Comments

Drag soldering works exactly as its name implies, by dragging a bead of solder across fine-pitch pins you can quickly solder an entire row. The method relies on clean joints, so liquid solder flux is often used to make sure there is good flow. But if you’re drag soldering on boards that you’ve etched yourself the solder can sometimes run down the trace, rather than staying where you want it. Professionally manufactured boards don’t have this problem since they have solder mask covering the copper that doesn’t need soldering. [Ahmad Tabbouch] has a method that uses Kapton tape to act as a temporary solder mask on diy boards.

The process involves several steps. First, three strips are place horizontally across the board, leaving just a portion of the upper and lower pads exposed. Those pads are then tinned with solder, and a light touch with an X-acto knife is then used to score the tape covering the vertical rows of pads. Once the waste as been removed, two more strips are added and those rows are tinned. From there the chip is placed and soldered as we’ve seen before; first tacked in place, then fluxed, and finally drag soldered to complete the connections. This achieves a crisp and clean connection, presumably without the need to clean up your solder mess with solder wick.

Kapton tape resists heat, making it perfect for this process. We’ve also seen it used on hot beds for 3D printers, and as a smoothing surface for sliding mechanisms.

[via Dangerous Prototypes]

Adjustable Prank Box Growls And Screams

April 3, 2011 by Mike Nathan 6 Comments

growling_altoids_tin

[Brett] over at FightCube was tossing around ideas to build a screaming prank circuit that fits inside an Altoids tin. Sound familiar? We featured a story just a few days back about the construction of a very similar item by [Dino Segovis]. It seems that great minds think alike after all!

[Brett’s] version is a bit more robust than the one we featured the other day. It’s similar to [Dino’s] in that it uses a 555 timer in astable mode, triggered by a normally-closed microswitch when the tin is opened. However, this version also includes a photoresistor which is used to increase the pitch and speed of the output as more light enters the box. This creates a growling effect that builds up into a scream as the box is opened. [Brett] has also included an adjustable pot which allows the sound range to be tweaked to his liking.

Stick around for a video walkthrough of the screamer circuit as well as a demo of the Altoids tin in action.

Continue reading “Adjustable Prank Box Growls And Screams” →

Simple DTMF Decoder Pulls Numbers From YouTube Videos

April 2, 2011 by Mike Nathan 28 Comments

dtmf_decoder

While many of us have banished land line telephones from our houses, there are still quite a few people who utilize POTS lines today. These analog phone systems use Dual Tone Multi Frequency (DTMF) signals in order to audibly represent all of the keys on a telephone keypad and place calls. [Brad] over at LucidScience decided that it would be useful to have a DTMF decoder on hand, and got busy building one.

His DTMF decoder box uses a CM8870 DTMF decoder chip, which you might assume is all you need to get the job done. This chip performs its duties very well, outputting a 4-bit binary code for each button press it registers, but that doesn’t do a whole lot of good without being able to represent those codes in a meaningful fashion. He first built a breadboard decoder circuit that would light 1 of 16 LEDs depending on the detected button press. This was well and good, but he decided that an Arduino-driven LCD display would work far better.

When he was finished, he had a compact decoder box with an LCD display, which accepts input from either an RJ-11 cable or an audio jack. He says that the audio jack is particularly useful for decoding tones from computer audio, such as YouTube clips. [Brad] praises the CM8870 chip, stating that it can pull phone numbers from pretty much any audio or phone signal you throw at it, regardless of quality. We think it would make a great basis for a telephone-based security system, if that was something that appealed to you.

Be sure to stick around to see his DTMF decoder circuit in action.

Continue reading “Simple DTMF Decoder Pulls Numbers From YouTube Videos” →