Adding RS232 To A Multimeter The Hard Way

November 12, 2011 by Mike Szczys 23 Comments

You might want to store information from a multimeter to be graphed over time. This comes with pretty much all of the high-end professional models. But if you buy a super cheap meter you can bet this isn’t an option. [Jazzzzzz] has found a way to pull the data from a $4 meter via RS232. It’s not impossible, but we definitely think he’s doing it the hard way. That’s because he’s not just tapping into a dormant feature. He’s actually adding a microcontroller to sample the data and push it via the RS232 protocol.

On the bright side, this is easier than building a multimeter from scratch. The sampling circuits are still being used, with a PIC 16F688 intercepting the signals as they enter the stock microcontroller. The signal he was after comes into the chip on just one pin, but to get the readings right on the PIC he had to use an OpAmp. That’s only part of the puzzle as he also needed a way to tell what the selector switch was set at. In the end, adding a potentiometer and reading its value let him calculate the position.

[Thanks Karl]

Adding Auto-off To A Cheap Multimeter

July 29, 2011 by Mike Szczys 24 Comments

[Florin] picked up a cheap multimeter in order to make multiple measurements at one time. Unfortunately, he wasn’t very good at remembering to turn it off when he was finished so he burned through some batteries. Why an auto-off feature wasn’t the first thing coded into the firmware we’ll never know, but [Florin] developed his own hardware-based auto-off circuit.

It sounds like he had all of the components necessary for this on hand already. He grabbed an AVR ATtiny25 in a surface mount package. To keep the board small, he didn’t include an ISP header, but instead made long pads that could have wires soldered to them for flashing the firmware. The microcontroller drives an NPN transistor that can cut off the ground path between the multimeter and its battery. A tactile switch is connected to one of the external interrupt pins and, when pressed, gives you 15 minutes of time to use the meter. After that, the chip kills the power and goes into sleep mode. Simple, and small enough to fit inside the case.

[via Dangerous Prototypes]

Hackaday Links: Tuesday, July 19th

July 19, 2011 by Jeremy Cook 8 Comments

Here’s another “useless machine” variant. The trick to this one is that it has dual “fingers” and can work either way. Which way it turns off is selectable via a switch on the side, and the fingers can both be turned on to “fight” each other. Check out the video here.

This video depicts the assembly of a Gameboy MAME-style cabinet. For those wanting to try something like this, this video may fill you in on some of the required assembly techniques, such as how to put decals on the side of your cabinet.

This video featuring the “Autonomous Ultimate Wall-E” shows this robot’s navigational skills around the house. Additionally, it has some nicely actuated arms.

The Verbalizer is a microphone designed to be used with Google’s voice search. It’s also designed with Arduino compatibility in mind and is open-source. Could be a good tool for your next hack.

These clever multimeter probes were built using pogo pins used in electrical test equipment. The springs inside of these pins help keep them planted firmly on the test point in question and reportedly gives a very good connection.

Lego Minifig Multimeter Makes Resistor Sorting A Lot More Fun

March 17, 2011 by Mike Nathan 21 Comments

lego_minifig_multimeter

While there’s typically not much room on our work bench for toys, [David] over at Robot Room has put together a pretty cool multimeter for which we would make an exception.

His Lego Minifig multimeter is constructed using mostly standard off-the-shelf Legos, and a pair of Minifigs he modified to suit his needs. Translucent Minifig heads were sourced online to allow the neck-mounted LEDs to shine through, and each of the bodies were drilled out in several places to accommodate the wires he uses to take measurements.

The multimeter will display the resistance of any item from 10 – 10,000,000 Ω, as well as measure the voltage of any battery you can manage to fit under the Minifig’s metal wrench. The multimeter takes measurements using an ATmega168, and relays that data through a serial to USB converter connected to a nearby computer. The computer is host to a .NET application he wrote which displays and speaks both the resistance and voltage values.

Keep reading to see a quick video walkthrough and a demonstration of the multimeter at work.

Continue reading “Lego Minifig Multimeter Makes Resistor Sorting A Lot More Fun” →

Make Presents: The Multimeter

January 26, 2011 by Caleb Kraft 17 Comments

This video falls under the category of things we want to send people when they ask “how do I get started with electronics”, and we get asked that a lot. For those of you who have been working with electronics ~~for years~~ at all, you can skip this entire video. That is, unless you really want to watch an instructional video on multimeters. In the video, which we’ve included after the break, they talk about the differences between different meters, the common uses and how to actually use the meter to get the results you need. Stuffed full of useful information, this video will get those of you who are still reading up to snuff pretty quickly. Now go use your multimeter to do some hacking!

Continue reading “Make Presents: The Multimeter” →

Building A Spectrophotometer

December 13, 2010 by Mike Szczys 15 Comments

What can you make with a toilet paper roll, duct tape, and a graphing calculator? A stand for your homemade spectrometer. This is neither as pretty nor as accurate as a precision scientific instrument, but that doesn’t mean it’s useless. In fact, it works perfectly well for rudimentary observations. Light is shined through a sample solution, passes through a diffraction grating, then shows up as bands of color on the projection surface seen above. The photosensor mounted on the cardboard tube was pulled from a night-light, and is read using the ruler and the multimeter. This results in two data units that are used to graph the results. As long as you’re running test samples as a control this simple setup will yield useful information for the scientist on a shoe-string budget.

[via BoingBoing]

Unlocking RS232 Serial Comm On A Multimeter

November 30, 2010 by Mike Szczys 20 Comments

[Craig] cracked open a multimeter to unlock RS232 serial communications that can be used for data logging. There’s a couple of things that make this possible. First of all, the multimeter’s processor is not covered in a black epoxy blob, leaving the pins exposed for hacking. Second, the chip model is known and [Craig] was able to get his hands on the datasheet. One of the pins enables serial output when pulsed low. Touching it to V- even turns on an RS232 icon on the display, as seen above. To make this accessible without opening the case a momentary push button can be added, as well as connector for signal output, and a bit of parsing on the PC side to handle incoming data.