Saturday, April 28, 2012

Bike helmet camera mount

Today I got a new helmet cam, a Contour Roam, but was not happy with the mounts that come with it, which rely solely on sticky tape to hold them to the helmet.  I designed and printed my own and published it on Thingiverse

Thursday, April 19, 2012

Bike horn

I’ve been riding with an AirZound air horn on my commuter bike for a couple of years now, and it’s pretty good but it is not durable.  It’s now almost totally dead, only working when the pressure is over 110 PSI.  Also they are known for not working in cold temperatures, below about 35*F.  This makes them useless for months out of the year.
I bought a car horn to put on my bike probably 7 years ago but it’s just been sitting around.  I finally decided to do something about it.  Here are photos of the (nearly) complete project.
This is the horn mounted on the rear rack deck with an L bracket using two #10 screws and nuts with lockwashers.  You can also see the saddle bag that holds the battery and 12v relay.
Here is the 12v lead acid cell and the relay.  The relay might be able to be skipped, but it’s really a good idea to use it.  The horn button really isn’t supposed to take this kind of load, and also you’d have to use heavier wire to go to the button.
I bought one of the standard type horn buttons available at any auto parts store:
I bent the tabs down so that they fit nicely alongside the stem on my handlebars, connected the wires to it, wrapped the stem with some electrical tape to insulate it, slid the tabs alongside the stem, secured through the tab holes with a tie wrap, then covered the whole mess with some old inner tube scraps and secured that with two tie wraps, like so:
The parts list goes something like this:
Car horn – $15 at auto parts store
Button – $4 at auto parts store
Relay – $7 at auto parts store
12v 1.8A lead acid battery – $14 on eBay
L bracket, nuts, bolts, wire, connectors, zip ties, inner tubes – Lying around or maybe $10 if you need to buy them.
You’ll also need a battery charger.  I have several lying around, but if you needed to buy one, for a battery this size something like a Harbor Freight float charger, which often goes on sale for $6, would be fine.
So this is probably a $40 to $50 project.  An AirZound is $25 and works really well if you only ride in warm weather.  It’s possible that an AirZound might last a long time if you took it inside in the winter. After two years on the bike mine is basically useless.
One note if you’re not so hot on electronics.  You need a battery capable of delivering at least 6 amps of current.  A battery the size of your pinky won’t run a horn even though it may be a 12v battery.  A batch of AA cells probably wouldn’t do it either.  Lead acid cells are really good at delivering high currents, and this tiny one only weighs a bit over one pound.  I think the whole thing probably weighs under 3 pounds.

Monday, April 9, 2012

Next project: Solar power!

I apologize for the haitus, it’s been quite busy at work, and I’ve also been doing some spring maintenance and grounds work at home.
However, I have my next experimental project lined up – I’m going to be building a PV solar panel from bare cells, building the frame to put them in, and hooking them up to a grid-tied inverter.  I want to see how much fuss is involved in this.  Prices have come down A LOT in the last couple of years, and I think solar is going to be a pretty big deal in the next few years.
If you’re not familiar with the term, a “grid tie inverter” takes power from the solar panel and converts it into AC power and feeds it back into the normal wiring that’s already in your house.(*)  This is a very exciting technology because it means that you can avoid what in the past has been by far the most expensive part of solar – you don’t need a room full of batteries, you don’t need to run a second set of wiring in your house to support low voltage appliances and lighting, you don’t need a whole lot of things.
What happens, then, is that the inverter offsets your usage, and in fact if the inverter is putting out more watts than you’re using, your electrical meter can run backwards.  Most US households use a few thousand watts (I hear that 5000 watts per household is a good working number, but if like me you’ve instituted conservation measures, and especially if you use gas for your various heating needs, it may be significantly less than that.
This is called “net metering” where the meter reads the net amount of power you consume after you’ve fed some power back in.  If you have one of the new, digital power meters, they generally will NOT run backwards, they’re “greedy” and are programmed to not give you credit for power fed back to the grid.  In some states and some power companies, they will actually install a second meter to measure power that you have fed back into the grid.  Of course, in those cases you do not get paid full retail, so they may be charging you 12 cents/kwh for power and only paying you 8 cents/kwh, so if the rules allow, it makes sense to divert some of your solar output into offsetting your own use before feeding any back to the power company.
In its simplest form, you just plug the inverter into a normal wall socket, hook up the solar panels, and you’re done.  I’ve even seen photos of panels just propped up in living room windows.
(*)  These are SPECIAL INVERTERS that are designed for this purpose – don’t think that you can go to the store and buy a camping inverter and plug it in – bad things will happen if you do that (as in bad things that may involve fire trucks and emergency services and not-at-all-amused insurance companies).