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Quick Intro

I'm a member interested in learning new stuff, helping improve SplatSpace, and returning to hobby electronics/programming. I have MSP430 Launchpads and an Arduino for the latter.

ECE Workbench Power Supplies

Part of a a basic complement of features for an electronics/computer engineering fab/debug workbench has to be a usable combination of DC power supplies. We need to be able to get the right voltage to a device with a wide range of connectors and avoid having to stop and fabricate a custom solution before the actual project can even start.The existing 0-30V variable bench supply provides a near universal solution (for supply voltages positive in relation to ground), but many people will be nervous using a supply for which total destruction of the equipment is just one accidental knob-turn away. That is, the variable supply will be very useful for short term, specific custom supply needs, but human factors prevent it from being a solution for (as an example) powering a Raspberry Pi for an extended period. The variable supply also only provides one voltage at a time. A dead-common scenario for the ECE workbench will involve equipment using both 5 and 3.3 volts, for example.

The obvious solution is a collection of fixed voltage DC supplies, and for positive supply voltages the existing 13.8V@10A supply is an obvious choice for deriving additional supply voltages. In combination with a similar "master" negative supply all of the commonly used supply voltages can be derived with both current limiting and short circuit protection.

An alternative approach is using a PC power supply to get many of the common supply voltages (+/-5, +/-12, and +3.3V). Current limiting is an issue, however, as even modest PC supplies will simply vaporize typical prototype electronic circuits if one of the voltages is shorted. The [[1]Dangerous Prototypes ATX Breakout Board] offers current limiting and very convenient termination with a few tradeoffs, the chief ones being too much limiting (1.25 amps) and omission of the -5 supply (that turns out to be the very first negative voltage I desire for one of my projects!). But this ATX breakout is so inexpensive that adding one to the ECE workbench seems like a no-brainer. Apparently marginal ripple current control, if it is an issue, can easily be dealt with by adding a few components to the board.

But 1.25 amps is simply inadequate for 5 volts, period. One project I have in mind will use one Raspberry Pi and two Arduino Unos. Although the 5v current requirement of an Uno is unpublished (yep, seems crazy, but this spec is no where to be found), but my best estimate is a couple hundred milliamperes if the Arduino is driving LEDs, servo motors, and what not. The Pi requires .7 amps assuming no use of its GPIO. Murphy's Law guarantees the ATX breakout polyfuse would trigger 92% of the way into my project. Finally, if we think just slightly past Arduinos we immediately see the need for greater supply currents. For example just about anything with an FPGA in it.

One obvious solution is to simply use a PC ATX power supply and stick a slow-blo fuse in it to avoid the "turn 24 gauge hookup wire into light bulb filaments" scenario. It turns out I have a very nice little fuse box in my amateur radio station that is underutilized. It uses relatively cheap automotive fuses. So I'm tempted by this.

On the other hand, I've partially completed a regulator that uses external pass transistors in combination with a three terminal linear regulator to form a 5-6 amp supply that is immune to shorts. So I'm in conflict.


This is about improving the situation with letting folks in the basement know that somebody is at the front or back building door wishing their cell phone battery wasn't dead, that the room phone was actually working, etc. This is not about upgrading the main basement room door lock with the Doorduino Project. As far as I can determine this work isn't competing with other work with Splat Space.

  • Update. Discussion with Justice Peters dampened enthusiasm for the doorbell approach and promoted a complete alternative using a third building entrance. Group discussion is needed to decide on whether the approach below is of any use.
  • Overall design. I propose making the doorbells with pieces and parts that have low technical risk. But the basic idea is that folks will press a spot on the door or window glass and this will latch on annunciators of some sort in the main 'Space room and the conference room for some period of time with some means of indicating "front or back", resetting itself if "nothing happens" for a period of time. Near the "door bell button" will be some indication that the button has been pressed and someone is being requested to come to the door. The person answering the door will reset the doorbell if it's still latched on. There's a lot of leeway for specific behavior: this is just a rough outline. Oh, and power consumption should be low enough that we just have to fiddle with recharging every few weeks at the most. The circuit should of course have a nagging mechanism to make it clear the recharge needs to happen soon.
  • Building Blocks
    • Wireless doorbells. Using standard wireless doorbells seems wise, as these use a very unusual frequency band (315mhz) that doesn't have any competition, support for multiple doorbells close to each other is built in, etc. Peter Reintjes tried exactly this solution, but the range wasn't sufficient for the signal to get into the basement from one of the doors (the back, as I recall). So that calls for something else:
    • High gain antenna(s). I've had a lot of experience designing custom antennas and doing various other RF projects (I'm licensed with callsign AD4L). I'm confident I can tremendously boost the efficiency of the radio side of things.
    • Something to Push. Hmm, we can't put a doorbell switch where somebody can reach it from the street or back lot. So something that operates through the glass is a must. It so happens that some of the TI MSP430 mixed signal microprocessor chips implement capacitive touch switches directly. It's must a matter of forming a capacitor with some metal foil and arranging for it to rest against the glass. I demonstrated how this would work at the April 21 Arduino meeting and at the April 24th regular meeting and it seems pretty reliable. The 430 chip can handle all other functions too, such as sensing low battery voltage.
    • Something to sense with. It seems irresistible to add an IR sensor that can notice somebody approaching the door and light up or otherwise show that the sign shows interest in return. Off the shelf IR rangefinders will operate through glass in most cases, so this seems straight forward.
    • A bit of glue. By glue I mean some hardware bits and pieces. For example, it isn't clear yet what's needed to have the TI chip "push" the doorbell transmitter button. Likewise, something like plastic suction cups or the like will probably be needed to hold the sign/capacitive switch in position. Add to this a battery, case, and maybe something to make it relatively difficult to steal the sign.
    • Annunciators. Various members expressed a preference for a relatively unobtrusive door bell. We don't want a loud "ding dong" in the middle of a meeting. Something low key and using light instead or light in conjunction with a soft sound would seem best, and annunciators of some sort need to be in the conference room too. Picking off the signal in the standard wireless doorbell receiver and disabling its sound should be straight forward. What the trigger will do is open for discussion, but I can start off with relatively bright LEDs and a sound we can live with.
    • Battery trickle chargers that are too trivial to use to be neglected. 'Nough said.
  • Implementation. I think I can prototype everything by borrowing the door bell from my house and combining it with the other pieces I have already in hand. Obviously the first milestone is to confirm my antenna building skills are where my mouth is. I have an idea for a touch switch made with a small piece of double sided PC board where I cut through the top trace to create a 12mm diameter disc (optimal according to TI) and drill a hole through the center to make a very low profile attachment to the disc. Using a TI MSP430 Launchpad (dev board) with the appropriate chip in it I can prototype the switch pretty well and test it with the actual building glass. The annunciator end of things seems trivial until/unless we want to get clever (voice of Hal?).
  • Drawings. Here's a partial schematic of an IR-based design for the xmit side. A few resistors are omitted. The key to this design is being able to independently power up the IR sensors and the doorbell transmitters when needed. This will hopefully keep the quiescent current draw on the battery very low. Using individual voltage regulators is out, as I don't own any regulators that have decently low quiescent current: 5ma seems to be the usual value, and to me that's way too high.

Splatbell xmit v.1.png


  • In the late 80s to early 90s I got very serious about homebrew beer brewing and I collected some books at that time. Below is a list of the books available to SplatSpace members for borrowing. The first dozen titles reflect my quick judgment/memory wrt wheat vs chaff, with the first two titles being supremo technical information. Titles 13 onward range from interesting/amusing to ancient British and American info-drek.
  • A few additional comments follow after the table.
Book Title Author Owner Borrowability Condition
Principles of Brewing Science Fix Pete Soper Okay Good (4/2012)
Brewing Lager Beer Noonan Pete Soper Okay Good (4/2012)
Yeast Culturing for the Homebrewer Leistad Pete Soper Okay Good (4/2012)
The Practical Brewer MBAA Pete Soper Okay Good (4/2012)
Homegrown Hops Beach Pete Soper Okay Good (4/2012)
Winner's Circle - 10 Years of Award Winning Homebrew Recipes American HB Assoc Pete Soper Okay Good (4/2012)
Beer and Brewing Volume 10 Loysen Pete Soper Okay Good (4/2012)
Beer and Brewing Volume 8 Thomas Pete Soper Okay Good (4/2012)
Beer and Brewing Volume 7 Thomas Pete Soper Okay Good (4/2012)
Beer and Brewing Volume 6 Thomas Pete Soper Okay Good (4/2012)
Best of Beer and Brewing Volumes 1-5 Association of Brewers Pete Soper Okay Good (4/2012)
Beer Judge Study Guide American Homebrewers Association Pete Soper Okay Good (4/2012)
Classic Beer Styles Volume 1 Pale Ale Foster Pete Soper Okay Good (4/2012)
Classic Beer Styles Volume 2 Continental Pilsner Foster Pete Soper Okay Good (4/2012)
Good Beer Guide 1989 Campaign for Real Ale Pete Soper Okay Good (4/2012)
A Dictionary of Pub Names Dunkling and Wright Pete Soper Okay Good (4/2012)
Brewed in the Pacific Northwest Meier Pete Soper Okay Good (4/2012)
The Essentials of Beer Style Eckhardt Pete Soper Okay Good (4/2012)
Home Brewed Beers & Stouts - Copy 1 Berry Pete Soper Okay Good (4/2012)
Home Brewed Beers & Stouts - Copy 2 Berry Pete Soper Okay Good (4/2012)
Brewing Beers Like Those You Buy Line Pete Soper Okay Good (4/2012)
Brewing Lager Alexander Pete Soper Okay Good (4/2012)
The Big Book of Brewing Line Pete Soper Okay Good (4/2012)
Pubs for Families CAMRA Pete Soper Okay Good (4/2012)
A Treatise on Lager Beers Eckhardt and McCallum Pete Soper Okay Good (4/2012)
The Complete Handbook of Home Brewing Miller Pete Soper Okay Good (4/2012)
Home Brewing - The CAMRA Guide Wheeler Pete Soper Okay Good (4/2012)
Boots Home Wine & Beer Making 1987-88 Boots (UK chemist shop) Pete Soper Okay Good (4/2012)
Beginners Book of Country Winemaking Turner Pete Soper Okay Good (4/2012)
Beginners Book of Home Beermaking Turner Pete Soper Okay Good (4/2012)
Beer Kits and Brewing Line Pete Soper Okay Good (4/2012)
Wine and Beer Making 90/91 Boots Pete Soper Okay Good (4/2012)
Better Beer and How to Brew It Reese Pete Soper Okay Good (4/2012)
Pocket Guide to Beer Simon and Shuster Pete Soper Okay Good (4/2012)
Hugh Johnson's Pocket Encyclopedia of Wine Johnson Pete Soper Okay Good (4/2012)
The Pocket Encyclopedia of California Wines Thompson Pete Soper Okay Good (4/2012)
The Signet Encyclopedia of Wine Henriques Pete Soper Okay Good (4/2012)
Home Wine Making & Brewing Boots Pete Soper Okay Good (4/2012)

Thoughts about beer brewing

  • The one area I'd still be very comfortable/eager to share about is yeast culturing. The first couple of titles above describe use of yeast cultures as present in commercial brewing settings that many homebrewers would consider impossibly impractical to duplicate (that is, a couple order of magnitudes larger than what you buy from Wyeast or manage to grow with a starter before you get paraniod about the purity). The yeast culturing title above and the others that touch upon hobby brewing yeast cultures were written before affordable high quality air filters were available. If you follow the yeast culturing book above you will often get contaminated yeast, in my opinion, because there is improper control over the air that feeds the yeast. However, if you arrange to pump the culture with STERILE air (in addition to strictly following other procedures for sterilization) then you won't ever get an infection and you can make a culture that will start your fermentation *immediately*, and I do mean immediately. This allows the yeast to get the upper hand in your wort and the random contamination organisms that slip past your sanitizing procedures will never get a chance to multiply significantly. (This is not an excuse to avoid meticulous sanitation, in my opinion, but everybody will draw their own line between how far you want to go vs tolerance for any off-flavors and/or aromas.) Together with starting my cultures from single yeast cells, my technique for growing several ounces of vigorous, healthy yeast for a pitch are one reason why I frequently annihilated the competition in homebrew contests and club meeting tastings.
  • Another major factor with respect to having a pleasant outcome with a beer brewing project is control of fermentation temperature. If you don't have a lot of money this translates to buying a used fridge and brute forcing it on and off with a thermostat that covers the necessary range for ale and lager fermentations. In my opinion if you stick the beer in the corner of a room and call that good enough, then by definition the beer you get will be good enough, but except for the most heavy handed styles that cover weird fermentation chemistry, the results will most likely never compete with the beer you buy. Getting the wort to the right temperature before pitching yeast and then holding the right temperature so the yeast experience the environment they were bred for is the second most important factor in brewing (after avoiding infection), in my opinion.
  • Hops grow like weeds in decent soil here in North Carolina. I've had hops grow around and up a 25' tall string so fast that with a magnifying glass I could see the growth! Perceptible growth is spooky, but then it's a real thrill. Properly drying the hops to the right percentage of moisture, vacuum-sealing them, and keeping them frozen until ready to use can drastically cut the cost of home brewing. Japanese Beetles, however, are the curse of hops growers in this area some years. I once drew so many beetles away from my hops plants that I filled a couple big paper grocery bangs with their carcasses. That's a lot of stinking protein! My neighbors all thanked me for drawing every beetle within a mile to my yard vs causing them any bother. If you're into this hobby for the long haul, think about adding milky spore to your property and some of your neighbor's property to eventually control the beetle population during otherwise "bad years."
  • High quality malted barley is available in big (50-60 pound) bags, and together with a decent mill, can noticeably reduce the cost of home brewing and bring styles of beer into reach that would otherwise be out of the question with kits. A decent mill is hard to come by, though, and getting the right, repeatable grind for repeatable mashing and sparging is simply difficult in many cases. When I was into brewing in the Triangle very few folks were doing all grain, but hopefully the value of this is obvious now and perhaps a "club mill" that could be shared by area enthusiasts is practical. Buying big bags of pre-cracked grain that was processed by a proper commercial mill is an excellent alternative if you and your brewing buddies can arrange to use it up fast enough: it cannot be stored for very long. The point of this and previous sections is that although this will (once again) annoy Mike Williams for me to say it, a batch of top quality beer can be made for a small fraction of the cost of a "kit." (Mike and I were very close friends when I was active: don't take this the wrong way. I was delighted to find that Mike is still around and his American Brewmaster web site looks great.)