Two of the items I picked up are for just that: a broken HP laptop and iPod/iPhone stereo docking station. They were a few bucks each, and I already tore apart the laptop for parts. The dock hasn’t spilled its secrets to me yet, but it looks pretty interesting. For this post, however, I’d like to showcase the main catch of the day: a Micronta digital multimeter and related accessories (including backup accessories as well!). Everything came haphazardly packed into a well-loved leather case for 15 bucks:

The case is a lost cause, but its contents are all in great shape:

Highlights of the pile include the multimeter (Model 22-195), a logic probe and pulse kit (Models 22-304A and 22-303), multiple sets of probes and clips, and even a “Dynamic Transistor Checker” (Model 22-025).

The multimeter is especially useful to me because it fills several holes in my arsenal of tools. It can measure the current drawn by a circuit (very useful for maximizing battery life) and has a good form factor for benchtop use. The meter I currently use is a handheld model, but I almost always use it at my workbench, so it would be easy to switch to a stationary one. The Micronta meter also oozes vintage look and feel, and I’m definitely enjoying the “lab” vibe that I get from it.

The “Logic Pulser” allows you to send a simple input signal to many basic chips. The “Logic Probe” allows you to monitor an output of one of those chips. Using the two together, you can test the inputs and outputs of multiple chips quickly and easily. These are a little dated now, but many of the logic chips this tool set originally targeted are still used, especially in the hobby electronics market (including the digital logic chips of the 4000 series and 74hc series). There are often times that I need to send a simple pulse signal to some of my chips, so I’m glad this set was included in the case.

The extra test leads were also a welcome bonus. I got several “clip” style leads. Each of these has a little, spring-loaded hook that can be extended from the tip. I didn’t have any before this kit, but they seem like they’d be super helpful with testing and breadboarding. Here’s a closer look at the leads:

Definitely a successful haul in my opinion. I have several “new” tools at my disposal. I’ll be integrating the multimeter into my work area this week. I’ve continued to work on the analog board I wrote about in my previous post, so look out for another post regarding that project. Thanks for reading!

More and higher resolution photos can be found in the photo album for this week’s haul:

Weekend Haul 1

I picked up several seven-segment displays a while ago; long enough ago that they have a cozy spot in my parts bins. Each module has two digits. I’ve been trying to incorporate them into something lately, and I decided to see what/how many I could fit onto a board:

I’ve also been trying out several different sensors lately (light sensors, microphones, etc.). I don’t really have a quick, easy way to measure their output without hooking them up on the breadboard and checking with my handheld meter, which can get pretty cumbersome depending on the situation. Being able to read, analyze, and log signals would be really helpful.

So a project framework and goal emerged. I have numerical displays and a need to display sensor values. From there, I started adding parts and connections in a “design-as-you-go” fashion. I felt very driven once I started this project and put a lot of work into it over the weekend. (I like to closely consider my puzzle pieces before setting them all down in a rush of activity.)

Here are some images of it in partial assembly:

I had a little trouble deciding which microcontroller to use. The ATtiny261 is small but still has 8 analog inputs; I had initially planned to drive the display with one. However, in the end the ATmega328P won out. It has more pins in total, which makes it easier to drive the display and still have plenty of input pins. Additionally, the ATmega has a built-in Serial interface that I hope to use to send commands/sensor data to a desktop computer.

I hooked it up with a test program as soon as I had completed enough to do so. Initial tests were done before the programming connector was finished, so I programmed the chip on another board (an Arduino) and transferred it to my board for the first few test runs. Here’s a shot of the board taken before the Atmega chip was installed:

Further tests went well, and the project has became more centered around the programming of the software than the hardware. I posted my first YouTube speaking role in the form of a video displaying a test version of the board:

Future posts will include how the display is driven and how the analog input section reads the values.

Here’s what I had at last post:

I finished wiring around the two sockets (destined to hold 74HC595 shift registers) and the result looks like this:

These shift registers are connected so the carry-output of the first feeds into the serial input of the next. This setup “cascades” the two registers so that they can operate as a single 16-output register, all controlled by a set of 3 wires. This concept is the basis of a huge multitude of projects in the hobby electronics world, since it allows the control of many outputs (16 in my case) through just a few wires. You can keep adding shift registers, with the only limit being how long it takes to shift out all the values.

Here’s the schematic for that board:

Each set of 4 output pins labeled “SIGNAL_OUT” is connected to pin headers that stick through the board to the one beneath. In this way, this board plugs into the board below it. The signals are then amplified by the transistors below to drive the LEDs.

Here’s the bottom of the board:

And viewing from the side, you can see the signal and power pins sticking up:

A view of the top (control) board partially inserted into the bottom (driver) board:

And here they are connected/stacked, and ready to hook up:

This module will control and power 16 channels of LEDs, and only needs 3 inputs (besides power/ground). I’ve done some preliminary testing, and it looks like it’s working great. I’ll work on getting some videos of the LEDs in action for a later post.

Button cell connectors for breadboarding – Hack a Day

I recently received several CR2032 lithium batteries, so we’ll see how well it really works.

Each row of five can get pretty bright, but I never got around to building a driver board utilize them. (Partly due to the face that I didn’t want to do PWM dimming on 16 channels with what I had at the time.) The five LEDs in each group are wired in parallel. The eight groups are arranged in common-cathode fashion, which means there are eight “power” wires and one ground wire on each board. Here’s a close-up of the end of a boards:

I received some new prototyping PC board recently, and it seemed a perfect opportunity to build a driver board for these panels. I decided to power each channel with a 2n2222 power transistor, with an 18 ohm current limiting resistor. This puts about 80 milliAmps into each LED channel, which should be quite bright. I drew up a sample circuit for one half of one of the boards’ drivers:

This circuit is basically repeated four times on the driver board. The outputs go to a 2×4 set of pins that the panels can plug into. The signal inputs (base connections) to the transistors are headers. Here’s how it turned out, top and bottom:

I’m really happy that I was able to fit everything and maintain a low profile. This lets me stack another board on top of this one with the control circuits. The next step I’m working on is a set of shift registers (74HC595) to control the panel signals. This could lead to controlling all 16 channels with just a few outputs of a microcontroller. I’m not far on that board yet:

Anyway, hope you enjoyed the photos. I’ll get some images/video of the LEDs in action once I have the top board a bit more populated.

I’m still learning the template, but it’s way better than reinventing the WordPress wheel just to get some blogging done. (WP really is pretty awesome for the amount of setup required.) Now I need to focus on content rather than structure for my updates.

For a little background, I’ve been switching my overhead lights with an outlet strip, with another strip nearby for “the brights”. I have some other power adapters and tools that I manually plug into these strips when needed. No doubt, this could definitely be a useful peripheral as-is, but it looked like it had some highly exploitable free space in it’s case. This led me to investigate (and plan) further.

The inner case has a large middle section that’s empty, save for the wires carrying switched phases heading back to the outlets. This section has over an inch of clearance, so I started thinking about what power supplies I had the parts to build. That’s plenty enough room for some proto board with some regulators on it (reminds me of the phrase, yak shaving).

As an alternative to building a power supply from scratch, I went through my orphaned/extra/funky wall rats box, and I hit gold! I found a 5V/12V switching power supply I had sitting around, probably from an external CD burner that no longer exists. It’s slim and will put out 1.5 Amps to outputs of 5 and 12 volts, so it’s next step in life will be to join this power bar.

Here’s the power bar (you can see the 5/12 volt supply already partially integrated):

If this is to be a bench supply, I’ll need some way of getting the power out. I started planning a set of jacks or panel on the left side, which led to the need for a set of features that I wanted in my supply. I like to “shoot from the hip” sometimes when designing circuits or gadgets, but I want to use this supply for  a long time without much modification. I think setting just a few key features will help get me a reliable tool (and get it out of the “in progress” box sooner). Here’s what I’ve come up with for a set of outputs:

• 12 volts on 2 or 4 jacks, with at least one switched – I don’t use this much, but I’d like to have access to it for robotics or car projects.
• 5 volts on several jacks, with some switched – This is my standard voltage, so I want to power my breadboard, as well as nearby stand-alone projects.
• 5 volts on USB jacks (female A) – I power a lot of projects from USB cables, and I don’t necessarily want those all powered from my computer’s ports.
• 3.3 volts and/or a variable voltage – Sometimes I work on 3.3 volts in low-power systems, but I need it seldom enough that a variable voltage output would be more practical.

It looks like I’ll need the circuitry to provide these power levels, and the panel & jacks to interface it to the world. Using the manufactured power supply and an old powered USB hub already covers most of the features. I have some LM317T variable voltage regulators, so I’ll build the variable output from that. Maybe that’ll satisfy my need to build part of it from scratch? I’ll see how I feel after the panel of jacks is completed and installed in the power bar.

I began this post intending to describe and disassemble the USB hub that I have in mind for inclusion, but I think I’ll build the next post around that. For now, here’s the powered USB ports that’ll be on the side of the unit:

• Breadboarding – Easy to make/use
  gadgets for prototyping on standard breadboards
• Lighting – LED lights/arrays, small to large rigs, and
  the circuits to control/power them
• Microcontrollers – Atmel AVR chips driving most of my
  projects

Lighting is pretty broad, so I may
have to split that up. On the other hand, most of the projects will
also be cross-referenced under microcontrollers, so that may become
a redundant category. I think I’ll have to see how my content
shapes up to build a more useful category structure. I might also
be misusing the WordPress term ‘category’, and if so, this process
may change altogether. Next step for now will be to get a little
actual content ready, with some photo documentation.