Add a Bluetooth Interface to Your Kitchen Scale

Kitchen scale

When [Adam] found himself in need of a force meter, he didn’t want to shell out the cash for a high-end model. Instead, he realized he should be able to modify a simple and inexpensive kitchen scale to achieve the results he desired.

The kitchen scale [Adam] owned was using all through hole components on a double-sided PCB. He was able to easily identify all of the IC’s and find their datasheets online. After doing some research and probing around with a frequency counter, he realized that one of the IC’s was outputting a frequency who’s pulse width was directly proportional to the amount of weight placed on the scale. He knew he should be able to tap into that signal for his own purposes.

[Adam] created his own custom surface mount PCB, and used an ATMega8 to detect the change in pulse width. He then hooked up a Bluetooth module to transmit the data wirelessly. These components required no more than 5V, but the scale runs from two 3V batteries. Using what he had on hand, [Adam] was able to lower the voltage with just a couple of diodes.

[Adam] managed to cram everything into the original case with little modification. He is now considering writing an Android application to interface with his upgraded kitchen scale.

How To Laser Cut Mylar Solder Stencils

Solder Stencil

When you think about the difficulties of working with surface mount components, the first thing that often comes to mind is trying to solder those tiny little parts. Instead of soldering those parts by hand, you can actually apply solder paste to the pads and place all of the components on at once. You can then heat up the entire board so all of the parts are soldered simultaneously. It sounds so much easier! The only problem is you then need a solder stencil. You somehow have to get a thin sheet of material that has a perfectly sized hole where all of your solder pads are. It’s not exactly trivial to cut them out by hand.

[Juan] recently learned a new trick to make cutting solder stencils a less painful process. He uses a laser cutter to cut Mylar sheets into stencils. [Juan] appears to be using EagleCAD and Express PCB. Both tools are available for free to hobbyists. The first step in the process is to export the top and bottom cream layers from your CAD software.

The next step is to shrink the size of the solder pads just a little bit. This is to compensate for the inevitable melting that will be caused by the heat from the laser. Without this step, the pads will likely end up a little bit too big. If your CAD software exports the files as gerbers, [Juan] explains how to re-size the pads using ViewMate. If they are exported as DXF files, he explains how to scale them using AutoCAD. The re-sized file is then exported as a PDF.

[Juan's] trick is to actually cut two pieces of 7mil Mylar at the same time. The laser must be calibrated to cut all the way through the top sheet, but only part way into the bottom piece. The laser ends up slightly melting the edges of the little cut out squares. These then get stuck to the bottom Mylar sheet. When you are all done cutting, you can simply pull the sheets apart and end up with one perfect solder stencil and one scrap piece. [Juan] used a Full Spectrum 120W laser cutter at Dallas Makerspace. If you happen to have this same machine, he actually included all of the laser settings on his site.

Reflow Oven Controller with Graphic LCD

Reflow Controller

A reflow oven is one of the most useful tools you will ever have, and if you haven’t built one yet, now is as good a time as any. [0xPIT's] Arduino based reflow oven controller with a graphic LCD is one of the nicest reflow controllers we’ve seen.

Having a reflow oven opens up a world of possibilities. All of those impossible to solder surface mount devices are now easier than ever. Built around the Arduino Pro Micro and an Adafruit TFT color LCD, this project is very straight forward. You can either make your own controller PCB, or use [0xPIT's] design. His design is built around two solid state relays, one for the heating elements and one for the convection fan. “The software uses PID control of the heater and fan output for improved temperature stability.” The project write-up is also on github, so be sure to scroll down and take a look at the README.

All you need to do is build any of the laser cutters and pick and place machines that we have featured over the years, and you too can have a complete surface mount assembly line!

Manual Pick and Place

picknplacePopulating a large surface mount PCB can take forever. [craftycoder] from Freeside Atlanta has built a great looking manual pick and place machine, removing the need for tweezers. No more will passives stick to your tweezers while you are trying to place them on your PCB!

We have seen a lot of pick and place machines in the past few years. What makes this one stand out is its simplicity and the no-nonsense build. This pick and place is built on an MDF platform, uses bearings from Amazon, standard 12 mm rails, and has a small camera for a close-up look at your part placement. Sure it is a manual method, but it beats painstakingly placing each part with tweezers. It would be interesting to see how much this entire build cost; we expect that it was not too expensive. See this thing in action in the video after the break.

We hope this project has inspired you to go out and make something cool! If so, let us know what you have made!
[Read more...]

This SMD Reflow Hot Air Gun Hangs Around Your Workbench

smd_reflow_hot_air_gun_nc_80

Has reflowing surface mount components got you down? [Giorgos] is currently working on a project that will lift your spirits…. well at least your hot air gun. Tired of manually holding his heat gun in one hand and IR thermometer in the other, [Giorgos] set out to create a device to alleviate just that. Although not completed yet, it appears the machine’s intent is to hold the heat gun at an appropriate height above the work piece in order to achieve the correct reflow temperature. He doesn’t say how the height of the hot air gun will be controlled. We’d like to see a microcontroller adjust the height of the hot air gun depending on the temperature of the component to be reflowed. [Giorgos] gives an extremely detailed account of his build process. Make sure to check out all four pages of the project post!

We’ve seen a lot of interesting work from [Giorgos] over the years like this capacitive touch-pad entry system.

[via Dangerous Prototypes]

Electric skillet reflow soldering guide

skillet-reflow-tutorial

It’s no secret that we’re bizarrely drawn to macro videos showing solder paste during the reflow process. This electric skillet reflow guide provides the fix we’ve been jonesin’ for while including some helpful tips for first-timers and veterans alike. Not sure what we’re talking about? Look at the grey paste at the top of this image. As it heats up it’s drawn under each component as seen in the lower half of the image.

This particular guide is aimed at one-off assembly so a solder paste stencil is not used (we learned a lot about those earlier in the month). It instead uses the painstaking toothpick application technique. It takes time but the upside is that once you get the hang of it you’ll apply the perfect amount of solder each time. After placing all of the components [Count Spicy] carefully transfers the board to an electric skillet, covers it with the glass lid (so he can see what’s going on), and sets the temperature just above the solder’s specified melting point.

Since the skillet is cheap and easy to find you really just have to order the solder paste to get into this type of assembly. Our only gripe is that you can’t really follow a temperature profile with this rig. For that you need to move up to some PID controlled hardware.

[Read more...]

Quick fixes for SMD population problems

quick-fixes-for-poor-PCB-work

Here’s a collection of tricks to get over some surface mount prototyping issues the next time you find yourself in a bind. But first we have to address the soldering atrocity seen on most of the components above. [Rxdtxd] admits he’s using a firestick for soldering his SMD parts. The non-brand 40W iron is just about the worst thing he could be using (well, we guess a candle would be worse). Try to overlook those joints and enjoy his solutions to a couple of other problems.

First up is what to do when you lift a fine-pitch trace like would be found on a TQFP footprint. The fix for this is to grab a junked transformer and use a bit of the enameled wire from the wrappings as a jumper. The wire is quite fine, and the insulation will burn off when soldered which means you don’t need to strip it first.

The second and third tricks both deal with resistors. As you can see above he placed two 1K resistors on a single resistor footprint to make his 2k resistor. The 0603 packages were both soldered standing on end, then connected with a lead from a through-hole component. The other resistor hack piles five components on top of each other to build resistance in parallel. This is not a great idea as it will fail over the long-term, but it will get you though the prototyping stage as long it doesn’t require precise tolerance.

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