Posts by horsham_sparky
78 posts • joined Wednesday 15th December 2010 17:01 GMT
Re: pressure switch
the way you might do it would be using a watchdog on the electronics that powers a normally closed relay which is in series with the pressure switch. i.e. if the watchdog is cleared regularly it powers the relay and keeps it open, thus preventing the pressure switch from firing the rocket.
If the electronics fails to clear the watchdog, or loses power completely, the relay automatically closes (they're spring loaded and need power to hold 'em open), and allows the pressure switch to kick in at the correct altitude.
The caveat being the software needs to be well written to ensure it doesn't arbitrarily keep resetting the watchdog (a common mistake when implementing watchdog monitors)
you could also have a seperate radio system to close the relay to allow the pressure switch to fire the rocket.. all of it is extra complication of course, it just depends if you want to allow the balloon to burst without firing the rocket (for a re-try for example)
Re: pressure switch
Give me a shout if you don't get any luck, there are other companies that do these things. I can probably blag a sample if push comes to shove through my electronics Biz :-)
Re: Gravity detector
I think you might snag yourself something larger than a duck were that to happen :-D
Still, a pint (or three) will solve any problem in existance.. world peace, starvation, cold fusion, and also why bags of nuts have that silly little label on them "May contain nuts"
In the words of Benjamin Franklin "Beer is proof that God loves us and wants us to be happy"
I'll drink to that!!!
Re: Any way the whole rig can be kept stable in free-fall?
stabilising fins might be more effective, simpler and will weigh less :-)
Re: Gravity detector
simples.. as long as it stays upright and doesn't get blown by turbulence close to the horizontal position ;-)
Re: "Failsafe" doesn't mean what you think it means.
The accelerator was meant as an example of a system that only "fails safe" if it stops performing a function (i.e. continuing to deliver radiation is an example of a system which does NOT fail safe), whereas the ventilator is the opposite.
You would hope the ventilator alarms and that someone reacts quickly enough to prevent serious harm to the patient, but that situation is definitely not fail safe! Having designed the electronics for a ventilator in a previous job, I can tell you that although the designs do include redundancy for critical systems, the pneumatics is arranged such that even under failure conditions it still provides positive air pressure to the patient. This is an example of a system that continues to provide a function under failure conditions
So perhaps I wasn't clear in last nights semi-drunken post (new batch of homebrew was ready last night mmmm), but in my own mind at least I wasn't confusing redundancy with fail-safe, but hopefully making it clear that fail-safe is a term that can have many meanings depending on what it is applied to :-)
Re: "Failsafe" doesn't mean what you think it means.
you're 100% right and at the same time 100% wrong.. yes that's contradictory, but please allow me to explain!
Firstly my background as self proclaimed expert (or nearest semi-expert in the vicinity), I work in medical electronics and have had formal training in safety engineering and much experience in designing stuff that is "failsafe"
you notice the exclamation marks (in real life I might have been making a funny gesture with two fingers)
you see, failsafe is all a matter of context. a rocket that fails to ignite.. has it failed safe? it depends if you're the bloke that has to approach it afterwards!
likewise, a linear accelerator that generates high energy x-rays.. it fails and continues to deliver radiation? definitely not safe! likewise a ventilator that helps a patient breath.. it fails and stops pumping gas into the patient.. is it safe? again definitely not!.
In this case, what the author means by "safe" is that the rocket is safely away from the balloon.. so if the main launch system fails, it has a failsafe backup that ensure the launch. Remember "safe" has many meanings depending on the context of the project
:-)
Re: dont know much about them but..
oh and p.s. its a mechanical switch.. i.e. its a mechanical mechanism that closes electrical contacts, much like what has already been discussed through various garden-shed arrangements of ice, bluetack, loo-rolls etc, however engineered by professionals (probably with lots of letters after their name, like Msc, Meng, Phd etc) to actually work :-)
Re: dont know much about them but..
I wasn't talking about a sensor (i.e. converts pressure to voltage), but a pressure switch (triggers the switch at a preset pressure level).. link again;
http://www.appeng.co.uk/product/psf101-ultra-sensitive-pressure-switches-with-fixed-set-points-spst-contacts
yes it has 20% tolerance, however on the 14.92mbar unit (approx 29500m), this equates to +/- 3mbar or around +/-1500m roughly. There are two ways around this if you need it better, firstly you set your primary electronic trigger to a level below this (say 27,500m), and make sure your burst altitude is higher than 31,000m
alternatively you can talk nicely to the manufacturer and get them to pre-select a unit with the right pressure trigger point for you :-)
Re: dont know much about them but..
actually, I already suggested a absolute pressure switch, set to trigger at the correct altitude (see the link in my post).
my only worry about the differential pressure switch on the balloon is how much differential pressure there might be between the balloon and atmostphere, and how much this will vary during ascent. The balloon expands because the gas inside is trying to equalise pressure with the outside world, so I would expect this differential to be quite small..
That said, it would probably spike before the balloon reaches the limit of its stretch, so maybe you could use that.. I prefer the set pressure method though, more predictable
pressure switch
Try something like this;
http://www.appeng.co.uk/product/psf101-ultra-sensitive-pressure-switches-with-fixed-set-points-spst-contacts
The manufacturer will set the pressure for you, calculate it to trigger above your main system pressure (allow for some error in both systems). If there isn't one with your exact pressure, you could use a differential pressure switch and put a known pressure on the second port. Looking at the one in the you can set it between 0.25mbar and 124mbar (30,000m altitude = 14mbar)
Again, why re-invent the wheel when there is already tried/tested tech out there that does it for you :-)
this gives you your mechanical solution you're after :-)
Re: Wireless charger?
glad that was only semi serious lol :-p
before I mention the weight of a magnetron.. or its power supply.. or the fact it would need more power than you can get out of a wee little battery (magnetrons aren't particularly efficient) or the effect concentrated microwaves will have on the electronics.. or metallic components.. in fact I'll stop there :-p
inductive heating might be slighty more efficient than the wireless power stuff.. however I think wireless power would allow you to have a lot more control over the heating. Not entirely happy with the thought of heating explosive compounds to begin with, but if you have to, then make sure its consistent, monitored and controllable :-p
I still favour a spring pin arrangement.. maybe combined with the magets to provide the coupling force.. hmmm
Re: Conductive rubber - or even just copper tape contacts on top of the rubber?
conductive rubber isn't all that conductive.. and the more resistive it is, the more heat it will dissipate.
Copper tape also corrodes very quickly, I wouldn't want to rely on it. (connectors are always flashed with gold for a reason ;-)
Re: Wireless charger?
There are off the shelf solutions for wireless charging, e.g;
http://www.rrc-wireless-power.de/en/products.html
However, these are limited in wattage (5W), and their range is limited. Using anything else requires some serious engineering.. which I suspect el reg don't have time for without sacrificing valuable pub time :-p
It might be do-able, with the wireless modules, you would have to give it a go and see
Posted in LOHAN fans drawn to magnetic coupling
Re: Why Re-invent the wheel?
In this case gold pads on a PCB would be OK. However if you need any significant amount of mating cycles, then the normal gold flash is insufficient as it wears away too quickly. In that case you need electroless gold over nickel plating (same as they use on the finger contacts on PCI cards), which is a much thicker and harder gold plating :-)
Another idea if the worry over the spring pins freezing is too much, you can also use battery contacts (like they use in smart phones). an example here:
http://uk.farnell.com/avx-interconnect/009155003201006/modular-battery-contact-3-way-3a/dp/1311148
might also be worth a look, though I've never used them in harsh enivornments, so couldn't vouch for the actual contact quality of these
Posted in LOHAN fans drawn to magnetic coupling
Re: Why Re-invent the wheel?
p.s. meant to say you can buy these from Farnell, about 50p each :-) don't forget to by the mating half, the contact pad is as important as the spring pin.
Posted in LOHAN fans drawn to magnetic coupling
Re: Why Re-invent the wheel?
We did environmental testing on these down to -10C.. can't remember what the humidity was (don't have access to the test reports anymore). The spring mechanism is pretty well sealed inside the unit, however if you're worried, you could always put a dob of low temp grease on the barrel immediately after soldering (this will drive out the moisture and guarantee the seal)
my best advice would be to get hold of some, do the above process and do some testing at representative conditions. Remember that putting a multimeter on it to test the resistance is not representative, you need to put the nominal load current through it and monitor that. (the reason being, high current will clean the contact area by arcing and vaporising any microscopic contaminants)
testing these things can be a project on its own! best to start with something engineered for job than a garden shed solution (sorry fellow boffins!)
Posted in LOHAN fans drawn to magnetic coupling
Why Re-invent the wheel?
There are already technologies for quick disconnect, the simplest and most reliable is spring pins, good example here;
http://www.mill-max.com/products/newproducts_detail.cfm?pid=84
The biggest problem which you've missed with the other "contact" solutions is these connections tend to fail or increase contact resistance with environmental factors (moisture, temperature, dust etc). Vibration also plays a big part, particularly when combined with the harsh environment LOHAN will be subjected to.
The spring pins are designed for reliable contact under harsh conditions, the special sauce being the hard gold over nickel plating, and the spring which applies a constant precise force to the contacts
I've got a lot of experience in this area, so feel free to get in touch ;-)
phew
I interviewed for Xyratex a while ago.. glad I found something else :-) Their products present some tough engineering challenges..
efficiency
The article derides the 80% efficiency as being too low to be practical.. the reality is that this is actually pretty good for a wireless system.Even with a wired system, you would be doing well to get 90% efficiency out of it. Less if you count the losses through the battery and charger (assuming the wireless system power is used dynamically rather than stored)
That said, yes its still more practical to recharge at stations.. the cost of implementing this on just motorways would be astronomical (anyone seen the price of copper cable these days?)
Re: What everyone in the industry knows already...
Where did you learn maths?
5V@2mA = 5V *0.002A = 10mW
assuming you meant Watt hours it would take 80 / 0.01 = 8000 hours or just under a year to get to 80Wh.. which would have cost you a grand total of.. *drum roll* 1.2p (15p per kWh)
p.s. sparky stuff is my day job ;-)
Re: CHP is a snare! @ Horsham sparky
Good points and well made :-)
Maybe I'm too much of an optimist and really want to see it working. oh well
Yep, you're right, inverters won't last forever, depends on the environmental conditions (they don't like heat), but I'd imagine there are clever ways to mitigate that (water cooling with a bit more overal efficiency as a fringe benny?). They can be made pretty reliable with well thought out and conservative design, it depends on the designer and the cost target.
I'm not so worried about the inverter issue as it can probably be resolved, however the fuel cell is the tougher target as the gas that's supplied isn't as clean as it could be and this can poison the cells if not filtered properly. if they can solve that one... :-)
Re: Remember that these switches are themselves in standby!
The problems occur when the device is switched when the mains is not on its zero crossing point, this leads to the surge currents discussed earlier. Only SSR's and other solid state devices allow this to be done accurately/reliably as mechanical relays are quite variable in their timing
So it entirely depends on the device and its design.. but the rule of thumb is you get what you pay for (i.e. don't use a cheap device on your £500 telly!)
and all of these devices will consume some kind of power (relay or SSR based), as they need some kind of active elements to look for the signals from the remote control to switch the TV back on. I'm not in the least bit surpised that this power can be as much as the TV's own standby current
Re: CHP is a snare! @ Horsham sparky
I brew my own.. so even more generated mwahahaha
Re: CHP is a snare! @ Horsham sparky
The thing I like about the CHP fuel cell units is that you're not in fact using any more gas than you normally would to heat your home. You're getting some free* electricity in the bargain.
However, if you read the original post, I said "when the tech is ready of course". Agreed that at the moment the expense vs payback period and service life probably doesn't justify it, hence why I inserted the above comment. That will likely change they perfect the technology in the coming years.. and yes someone (the early adopters as always) will pay for that so the rest of us get the benefits in a few years time
* these are likely to be more expensive than conventional boilers so not free if you count installation cost over a conventional boiler. but you reduce your leccy bill in conpensation.. whether thats enough to compensate is open to debate :-)
Re: annoying
Hope you've got that lot on a surge protector on that lot.. those remote switches introduce a surge every time they switch something on. A lot of modern equipment isn't designed to take the surges.
and remember surge protectors don't last forever, they get damaged by the surges as well. In the case of our telly it saved us a couple of quid in electric while it was working, but cost us £500 for a new telly!
Re: CHP is a snare!
Always nice to see such scientific well reasoned arguments based in fact :-p
if you look at the pattern of boiler useage its typically in the winter when people are at homes, with the lights on, TV/kettle on etc..so you don't necessarily need a good feed in tariff to see the benefits.
There are plenty of studies to show CHP will reduce energy consumption in the domestic environment, Ceres have a few on their website.
with regards to centralised generation, take a look at this part of their website
http://www.cerespower.com/ProductOverview/CHPOverview/
Re: actually
a couple of useful wikis;
http://en.wikipedia.org/wiki/Cogeneration
http://en.wikipedia.org/wiki/Micro_combined_heat_and_power
CHP systems are already used commercially to reduce energy bills, they just haven't made the domestic market yet
Re: actually
CHP uses gas like a conventional boiler. However it turns the gas into leccy with via the fuel cell with heat being a waste product.. but here's the clever bit, that waste heat is used to heat your water for central heating. so you use the same amount as gas you would normally, but you're generating free(ish) leccy at the same time.
Overall it makes more efficient use of your gas that any conventional boiler can, and with leccy from the grid being much more expensive than than the equivalent kWh of gas, you'll save a lot of cash overall
actually
If they really wanted to make a difference to UK leccy consumption, they should make CHP systems mandatory for all houses.. when the tech is ready of course. take a look at these guys for example
http://www.cerespower.com/
installing one of these will save far more leccy than worrying about standby power or hair furtling devices
annoying
my partner is always telling me to switch stuff off at the wall... last year we were given one of those automatic power off bricks that cuts off mains to your devices when it detects they're not in use, which she fitted to the TV
Unfortunately due to the crap design, the surges this thing introduced zapped my £500 telly within 2 weeks of use!
She got the hump when I told her that she could save 100s of times more leccy by not having the shower running 5 minutes before she gets in it.. "oh but I like it to be warm before I get in"
damn do-gooding-lacking-in-braincells-econutters!
Re: Douglas Adams as always ...
was just thinking that... yah beat me to it lol
Posted in Dimming the lights on smart(arse) TV
Re: sounds familiar
Nope, not come across them before sorry
I work mostly on Medical Electronics
Posted in Dimming the lights on smart(arse) TV
schoolboy error
Note.. my earlier post is still a useful response even if you DO know what's wrong with it :-p
Posted in Dimming the lights on smart(arse) TV
sounds familiar
Being a sparky (Electronics Engineer.. not an electrical engineer, and yes there is a difference!), I get the same all the time.. parents, partner, friends.. can you fix my (insert latest fad-gadge here)
Normally my response is "No problem! By the way, I charge £40 per hour.. because I don't have the schematics, BOM or any other information for it and I'm not likely to ever get it from the manufacturer, I have no idea how long it will take or even if can be fixed"
they reply
"£40 per hour!! I'd be better off buying a new one!"
to which I reply with a smug smile
"Yes.. you would!"
Re: Dyscalculia
I bet he chairs the DNA in his spare time (National Dyslexics Association)
OMG!
An expenses beancounter with a sense of humour? whatever next? hens with teeth? :-)
Re: wonderful
Agreed
But this is really a sticking plaster on the wider problem.. a properly thought out system and supporting process for patient records and management, that's unified for all hospitals.. I wonder how many times this wheel has been re-invented?
There are huge savings available if only they could get a decent system in place.. £150k p/a is barely enough for another doctor
wonderful
So the NHS is up to the 90's in terms of technology... whatever next I wonder?
Re: Am I the only one with the urge to say ARRRRH!!!!
yes, but the rest of us managed to show some self-restraint.. :-)
That said, you've let the parrot out onto the shoulder..YARRRR!!! X marks the spot me hearties!
Re: i must have missed the IT angle
There's quite a bit of gold used on circuit boards, IC's etc inside computers..
OK, a slight stretch, but there's more to life than IT you know (beer for example)
Re: Searching over the same field for 30 years?
maybe someone saw a leprechaun and they were searching for his pot'o'gold..
guess they found it :-)
Re: Instead of moaning at stupidity, do something
Done.. no wonder people don't like consultation questions.. same question phrased 30 different ways!
dammit!
I knew I left them somewhere! :-p
Guess this is the early version of loosing your change down the back of sofa :-)
yet another well intentioned but misguided law in the making
Anyone remember anti-terrorism laws being used to stop photographers snapping the police, train stations, public places?
anyone care to speculate exactly what is meant by "harmful content"? I can see this being mis-used and abused as yet another form of censorship, that is ineffective at stopping the thing its meant to stop (i.e. stopping kids watching porn)
Any kind of controls the ISP's/Government put in is likely be easily bypassed by the kids who probably know more about the interwebs than these ministers!
An earlier poster had it right.. it's down to the parents to ensure they're in control of what their kids see, and to decide what is best for them.
Re: Electronics are going to be much more reliable
Sorry :-p well guess I should know this stuff seeing though I'm an Electronics Engineer... only mechanics I know is from A-level maths (I did Pure and Mechanics). I'm sure there's stuff you could teach me about fluidics, thermal flow, stress etc etc etc
Just goes to show, doesn't matter how much you know, there's always someone that knows more :-p
Re: Electronics are going to be much more reliable
try measuring the signal from a fuel cell (1mV full scale deflection), when you've got TETRA radio signals bouncing around (80V/m.. normal EMC test is 3V/m or 10V/m at the most) :-)
modern devices, properly laid out and implemented have incredible common mode noise rejection
Still.. ho hum, that's life
Re: Electronics are going to be much more reliable
Ahhh, University electronics.. those where the days
you problem was probably the prototyping breadboard.. lack of groundplane is normally what instrument amps don't like too much.
I've been using them without problems for years
pressure switch
or you could just use a commercial mechanical pressure switch like these :-)
http://www.impress-sensors.co.uk/low-range-pressure-switch.htm
Re: Electronics are going to be much more reliable
Sorry, you're wrong :-)
OK, partially right, but depends on the circumstance and device you choose
if your source is relatively low impedance (e.g. wheatstone bridge device like a strain gauge), then they're pretty stable and will work down to -40 C (industrial grade devices). They will typically consume less than 50mW (an AA battery has around 3Wh of power, so that would last 60 hours.. plenty of time to launch)
older devices are less stable and use more juice, but modern devices are pretty good these days
