Why not look at the (late?) Jim Thompson's hearing aid designs from the late 60s? Since that seems like approximately the era of tech you wish to work with. I think I recall reading someone here has preserved the documents, the sliding class A bias is quite well-explained.
The most exotic part you might need is an IC that has a matched pair of transistors on the same die they're not too costly or hard to come by
Or, in a pinch, match some TO-92s by hand and paste the packages together with a drop of thermal epoxy.
Sounds like a plausible project to me. Yeah digital hearing aids are great but they aren't magic, you need a trained audiologist and a bunch of fancy measurement tech to get them set up right for a particular person's hearing loss profile. I know I take my mother to have hers adjusted every six months or year or so.
Without the proper setup and a PC running some $8000 software + test and ROM flash interface or whatever they're not really any better than a set of analog aids, maybe worse. Digital aids also seem very sensitive to any small wax buildup in the earpiece or tubes, need to be cleaned constantly.
Digital hearing aids sure shouldn't be suffering from acoustic feedback!
ote:
aid. But it's not something I've designed before. The musts:
you can get that only run a few days on coin cells. Using AAA or AA is poss ible.
one that would do this. The 386 has min 4-5v, Iq 4-8mA, hardly ideal, not totally ruling it out but don't love it.
AAA 0.3-0.5Ah at 8mA = 50 hours, and that's just I_q. No use at all.
ery low voltage amp design or with sliding class A.
ology is not likely to produce a useful design.
ADI makes a family called Sigma perhaps? I think TI has a very similar fa mily. They are intended for apps based on digital audio data so the archit ecture is designed to process a fixed algorithm on each sample, triggered t o start when the sample arrives. It's been a while so I don't recall the d etails other than they are very small, require little power and are under $
d. I haven't checked the other thread yet and probably won't bother.
I read his pdf on sliding class A. I_q is 0.7mA, the same as a 358, the oth er performance figures are generally better but the part count is high comp ared to a 358. So on balance I think I prefer the 358. I did consider desig ning a slider from scratch, but I'm not experienced with them, and the 358 is a quick & good solution. It's hard to get simpler, and simple means less time/cost to construct.
NT
Even if they didn't need any of that they're too expensive & require too many tools to build. None of that is workable with assemblers in shacks.
NT
I'm using Firefox 52.9.0(32bit) on Windoze XP (because I'm too lazy to move all my junk from XP to one of several nearby machines. Good enough for maybe another 6 months after which I'll probably switch to Linux.
I use quite a few of the utilities by Nirsoft including MZHistoryView. However, it's not really necessary.
My history file (places.sqlite) is currently 81 MBytes on this machine. That's about 6 months of browsing history. I use the history quite often and don't really want to erase it.
Thanks. Not everyone likes my rhetorical questions.
It's fairly easy to do Google searches and produce usable results. It is NOT easy to produce a fairly short link with the tracking info and previous URL's removed. In order to do that, one must understand how the various Google searches (web, images, patents) work. I took the time and trouble to reverse engineer the Google URL line so I could do this. I don't have time right now to write a tutorial on building a Google URL line, but some quick hints are possible:
Basic Google text search:
Basic Google text search where "design" must be included:
Google Image Search: My favorite "trick" is to use Google image search to find something appropriate or close, and then follow the image back to the original web page.
Google search operators: These are worth studying just to see what's available. The operator that I use the most is to search a specific site. For example, my site looking for something on the HP8640B:
Another trick is that I answer questions much in the same manner that I would expect someone to answer my questions. When I ask a technical question, I find that detail, derivations, examples, and links are quite important. I don't often get everything I want, but I do try to provide these to others when I answer their questions. One line position or opinion statements are not very useful.
Good luck and bug me if you want more of this kind of stuff.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
The $15 analog hearing aids that I've been buying for friends and customers on eBay certainly do have audio feedback. Oddly, the customers seem to like it. Just turn the volume up until it screams. Then back it off until it stops screaming to set the operating point.
Also, one of my friends went from a cheap analog hearing aid to a seriously overpriced digital BlueGoof hearing aid. At a recent meeting, I noticed that he was wearing his old analog hearing aids. The problem was the latency in the digital hearing aid sometimes caused a problem. It was mostly ok, but was long enough that if he tried to lip read at the same time, he would quickly become confused. The problem was his overpriced hearing aid used the original BT 1.x technology, which had considerable latency. I advised him to get something with BLE (BlueGoof Low Energy), which should be much better. Sorry, but I don't have latency measurements or model numbers.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Thanks for the helpful reply. I also use Firefox 52.9.0 since it is the last version that still accepts older addons. I'm running Ubuntu 10.04 and XP in Virtualbox. I love the combination of Linux and XP. I can run things in Ubuntu and XP simultaneously, and neither affects the other. Big help!
I constantly erase my history file so when I do a search, I always have a fresh history to save on that specific topic. When I am happy, I copy the history file to an ongoing text file for future reference. I'm not interested in saving ordinary links, such as news sites and other random links, so I erase them before starting a search. I find it very important to save the search history as there is often a very valuable link buried in there that I can never find again.
Yes, I would like very much to learn how you do your searches, and what kind of search strings you use. You come up with very useful information that I can never duplicate. Please post your search strings!
Thanks
I should mention that I also run Win7 in Virtualbox for the very few sites that won't load in XP.
Virtualbox allows you to run as many different OSes as you have memory for. It is very convenient to be able to switch between XP, Win7, my banking VDI's and Ubuntu at the touch of a mouse click.
Another great feature is the ability to copy the VDI to a backup disk. You get a byte-identical backup that you can run on other machines, or use it to restore a mangeled VDI, such as one that got ruined by installing some program that won't uninstall.
Yeah, nothing in this country is, or ever has been made, that is priced less than $70.
I thought it was $70.
That's exactly what I did. Your numbers don't pass the bullshit test.
Latency is a big problem for wireless headphones. I was looking for a pair of ear buds for use in the gym. The latency of some is just horrible (1-2 seconds on some). I can imagine it would cause problems with people who are hard of hearing. It caused me problems just watching NetFlix. Even a couple hundred milliseconds is a PITA.
Monolithic pairs are rare and expensive. Zetex had one but they've been assimilated.
Look for a BT transmitter and headset that support aptX: I haven't actually seen or tried aptX, so I can't testify that it works as advertised.
1 to 2 seconds is truely horrible. 50 msec is a good target, 100 msec is objectionable, and 250 msec is where users consistently complain.If you're watching Netflix on a computah, try these tweaks: "How to Fix Netflix Audio and Video Out of Sync"
If you're using VLC to watch TV, it has a built in lip sync tweak:
There are hardware lip sync correction boxes available: However, they only work when the video decoding is delayed behind the audio, not the other way around as in delays caused by Bluetooth.
Also, I don't think any of the aformentioned tweaks and solutions will do anything for a 1 to 2 second delay.
One reason smartphone customers are irritated with the manufacturers removal of the earphone jack from handset, and replacing them with Bluetooth equivalents is the resulting latency:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
That might work for most, but I can remember my grandfathers hearing aid squealing loudly and he couldn't hear it. We had to tell him to turn it down. I was young at the time, but, I suspect that means his hearing aids didn't do him much good.
Mikek
The cheap throw away hearing aids sold on eBay are not intended for severe hearing loss. The target audience are those who's hearing has slightly deteriorated over the years and are not ready for an expensive professional hearing aid. Whether that's a good idea is rather questionable as it would be nice to know the cause of the hearing loss.
If your grandfather could not hear the feedback squeal, and it was an "in the ear" type hearing aid, it might have been a bad fit to his ear. Keeping the mic and earphone acoustically isolated requires a good tight fit. When properly sealed into the ear, most (not all) hearing aids will not squeal. Custom earmolds are usually required if the hearing aid is set to a very high gain: Make your own:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Once everything's digital it's not hard to implement a feedback destruction algorithm in software; the incoming audio is passed thru an array of narrow digtial bandpass filters and the bands are monitored for energy spikes, if it starts feeding back you turn down the gain in the problematic band.
mind you those are the kind of features you'd expect on a set of digital aids in like the $4000/pair price range
bitrex wrote
It was done in analog hardware long time ago by using frequency shift:
so many problems go away when you let go of the miniature in/on ear format.
NT
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