Diagnose And Repair A Yaesu FT-7800 Ham Radio

November 11, 2013 by Todd Harrison 26 Comments

[Alan Wolke] aka [w2aew] was challenged to repair a friends Yaesu FT-7800 ham radio. This radio operates on two ham bands, 2 m VHF and 70 cm UHF. The complaint was that the 2 m side was not working but the 70 cm was transmitting fine. Alan started by verifying the complaint using a Bird watt meter with a 50 watt slug and terminating the signal into a 50 W dummy load. [Allen’s] bird meter is the type that has an RF sampler that can be connected to an oscilloscope for added signal viewing and validation.

After verifying that the radio was not working as described, Alan starts by glancing over the circuit board to look for any obvious damage. He then walks us through a block diagram as well as a circuit diagram of the FT-7800 radio before stepping us through the troubleshooting and diagnostics of radio repair. Even when he realizes he might have found the problem he still steps us through the remainder of his diagnostics. The skills and knowledge that Alan shares is extremely valuable to anybody looking to repair radios.

Spoiler alert. At the end of the first video he determines that the pin diodes near the final VHF output were bad. In the second video he reveals that he could no longer source these bad components. Through some clever evaluation of a more current Yaesu radio, [Allen] was able to find suitable replacement components. Lesson two ends with some surface mount solder rework tips as well as testing that the repair was successful.

And just in case you don’t know what a pin diode is, or is used for, Alan shares a third video covering just what this component is and does in a radio. You can follow the jump to watch all three videos.

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Build Your Own Desoldering Station On The Cheap

November 11, 2013 by Todd Harrison 34 Comments

[Sable Wolf] tipped us off to his DYI desoldering station for under $70. We know we have seen this conversion before, but it hasn’t been featured on Hack a Day. [Sable Wolf’s] hack is unique and has added features that make building, cleaning and the overall longevity sounder. However, some kind of sound deadening housing would have to be built around the pump as it seemed uncomfortably loud in the video.

Some Chinese made desoldering stations are getting quite cheap so maybe it’s not worth the effort unless you can salvage more components for the build. Thanks to [Sable Wolf’s] detailed blog you can browse through his BOM and scrounge up the majority of these items from your salvage bins. A cheap but reliable desoldering station would be an extremely handy tool to have on your bench.

This is much safer than desoldering with a candle or using fire as featured in the past, and is kind of a flip around on the SMD hot air pencil hack.

Follow long after the break to watch the video of the desoldering station in action.

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KiCad Video Series: From Concept To Manufacture

November 10, 2013 by Mathieu Stephan 37 Comments

Many of our readers took the habit of using Eagle to design their PCBs. Even if you’ll find plenty of support for this software as well as a lot of parts libraries, the software comes with limitations. The useable board area is limited to 4×3.2 inches, only two signal layers can be used and more importantly the schematics editor can only create one sheet. On the other side, some of you may already know KiCad, a free open source and unrestricted schematics and layout software. [Chris] just tipped us of a video series he made, showing people how to design and build their very first PCB using this software. It’s a simple 555 circuit, but goes through all the steps necessary to design a PCB that costs only $5 through OSHpark… and will blink by the end. All the videos are also embedded after the break.

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DIY Doggy Doorbell

November 3, 2013 by James Hobson 16 Comments

doggy doorbell

Is your dog the strong silent type? Ever wish he or she could tell you when it is time to go do their business? This Reddit r/DIY user found a simple solution — a doggy doorbell!

The dog in question isn’t very vocal, so his owner sought a simple solution, similar to Pavlov’s bells — the only problem? He needed some range on it, as you can’t always hear a few bells throughout the entire house. The solution? A wireless doorbell that he repackaged into a dog friendly button!

Compared to our last post on an automatic pet watering system, this one is a very simple hack that requires absolutely no electrical experience. It could be improved upon quite easily though, by wiring a second switch in parallel so the dog can ring the doorbell from the outside of the house too!

According to the owner, it only took a few treats to get the pooch trained well enough to use it whenever he needs to go out!

[Via Reddit]

DIY Pneumatic Skeleton And Air Horn Gag To Scare Those Trick-Or-Treaters

October 19, 2013 by Todd Harrison 13 Comments

[Rick Osgood] has been busy making more scaring gags for Halloween. This week he’s sharing great ideas for an air horn and pneumatic jumping skeleton, both actuated by 24 V sprinkler valves. These two new gags can easily be activated using [Rick’s] cardboard floor plate switch and three 9 V batteries cleverly snapped together in series for a 27 V supply (we can’t resist dropping in this link to a 2196 V supply from 9 V batteries just for fun).

The air horn construction is quite unique using a latex balloon strategically located as a reed valve for the air to vibrate over as it rushes out making a very loud honking sound. [Rick] then connected his manual bicycle pump to an air supply so that when an air valve is actuated the bicycle pump handle with a skeleton wired to it pops up. It then lowers back down via a bleed hole in the air line. Both the air horn and pneumatic pop-up skeleton seem simple to construct and his tests show them functioning perfectly.

Being the air storage chambers are small the re-trigger setup seems too repetitive to be practical for a continuous stream of Trick-Or-Treaters. Perhaps one could hide an air compressor with a long feed line to supply the gags? Plus, using an air compressor would come in handy for other scary blasts of air. Of course you would want to lower the compressor’s output regulator to safe levels so you don’t risk blowing apart your pop-up skeleton rig or any pipes.

Follow along after the break to see how to build these two great gags and get some tips from Mr. Safety.

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Build A Sensorless Brushless DC Motor Controller

October 19, 2013 by Todd Harrison 43 Comments

[Davide Gironi] shows us how to implement a sensorless brushless DC motor controller (sensorless BLDC) using an ATmega8 microcontroller. In order to control a BLDC motor you need to know its rotational sequence position and speed so you can calculate and apply the correct current phase sequence to the motor windings at just the right time.

Simply said, sensorless BLDC means you’re not using a purpose built sensor to determine the motor’s position and speed, however, you are sensing the motor’s sequence position using the back EMF signal coming from one of motor’s coils that is not currently receiving power. When this back EMF signal crosses zero voltage a microcontroller can calculate the rotational speed and when to switch to the next power sequence. This technique is not good for position control motors but is great for continuous motors like computer fans and drives were the slightly reduced wiring costs make this type of BLDC control favored.

If you want to build a BLDC controller we recommend starting with [Davide’s] last project on sensor controlled BLDC motors. You can also checkout these interactive demonstrations for more understanding on the different BLDC configurations.

Follow along after the break to watch the video demonstration of [Davide’s] sensorless BLDC controller controlling a motor from CD-ROM drive.

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DIY HHO Mini Torch

October 11, 2013 by James Hobson 52 Comments

Fascinated by hydrolysis apparatuses? Me too. Here’s a cool how-to that might convince you to make one! It’s a very simple and easy to build HHO torch using plumbing parts from the hardware store.

The entire build uses almost all standard readily available parts — except for the nozzle assembly. It’s an easy modification though, under the copper pipe endcap is a brass M6 nut that has been soldered in place – this allows you to switch out the MIG welding tips at any time.

[Peter] also shows off another useful tip that allows you to reduce the orifice size of the MIG welding tip – simply hammer a ball bearing into it. Seriously, check out the Instructable and see for yourself! This allows him to reduce the orifice size down to non-standard sizes which in turn allows him to increase the intensity of his HHO flame.

Now all you need is a source of HHO — but don’t worry, we’ve covered that before too!

[via Reddit]