DIY hearing assisting magnetic neck loop help - Page 1
Forum section: electronics / beginners

author: geratheg
author_rank: Regular Contributor
timestamp: January 01, 2016, 08:07:02 pm
content: I need help understanding some components in the schematic in the following link:http://archive.siliconchip.com.au/cm...6/article.htmlI know it might be outdated, suggestions for newer devices welcome. I'm going the DIY route just out of curiously and it being cost effective.I'm confused about two components:1. I don't understand what component ZD1 is assuming it's some kind of diode. I'm hoping to find some exact diodes to use for ZD1 or some suggestions would help.2. In the picture of the assembled schematic, some capacitors look like ceramic disk capacitors but others look like rectangular boxes. What kind of capacitors are those? Does it matter which kind I use? Also curious about why if you know.Thanks!

author: Simon
author_rank: Unknown
timestamp: January 01, 2016, 10:16:05 pm
content: It's a zener diode which will have a constant voltage across it, in this case 4.7V. To be honest I'm struggling to understand it's purpose and that of the whole branch of circuitry it is connected to.The "box" capacitors are likely to be film capacitors, they are higher quality but if this is all audio then ceraic will do as well. They should be specifying which is which if it matters.

author: wblock
author_rank: Regular Contributor
timestamp: January 01, 2016, 10:23:35 pm
content: Quote from: Simon on January 01, 2016, 10:16:05 pmTo keep the LED at a constant brightness as the battery discharges, isn't it? But that 470uF cap, and the 1N4148... Seems like that could be done better, or maybe just laid out more clearly.

author: SeanB
author_rank: Super Contributor
timestamp: January 01, 2016, 10:27:03 pm
content: ZD1 is a flash on power on circuit, which provides a brief bright light on power on, but which then glows dimply to remind you it is on. Also serves as a low battery indicator, as it will not light when the battery is flat. Using film capacitors is mostly because they are generally more stable than disc ceramic, so have lower change of capacitance with both voltage, temperature and time. The small ceramic ones are normally going to be specified as NPO so they do not drift much with time.

author: Simon
author_rank: Unknown
timestamp: January 01, 2016, 10:29:46 pm
content: well yes if all they want is a flash on turn on then yes but 27K is very high.

author: SeanB
author_rank: Super Contributor
timestamp: January 01, 2016, 10:35:34 pm
content: Bloody bright with modern LEDs and pretty much usable, and keeps the battery drain low. The problem with driving a LED at around 10mA with a battery is that often the LED uses more than the rest of the circuit. As your power source is a PP3 battery with really limited capacity keeping power use low is very important.The one shown will light up at blinding level for a second or so at turn on, then drop down to something more dim but still viewable. The zener simply means when the open circuit battery voltage is below around 6V it will not light at all. telling you battery is flat before the opamps stop working, though at 6V they will have higher distortion than normal.

author: geratheg
author_rank: Regular Contributor
timestamp: January 04, 2016, 01:16:45 am
content: I also contacted whoever wrote that article and here's what they said:"ZD1 is part or a battery indicator. It reduces the voltage so that the LED can show bright when the battery is 9V but very dim when the battery is below 7.2V."However, they haven't yet mentioned what type of capacitors were used.

author: geratheg
author_rank: Regular Contributor
timestamp: January 04, 2016, 09:15:21 am
content: So I'm considering buying the caps from tayda electronics and they have two film options:Polyester Mylar Film (http://www.taydaelectronics.com/capacitors/polyester-mylar-film-capacitors.html) andPolyester Film Box Type (http://www.taydaelectronics.com/capacitors/polyester-film-box-type-capacitors.html)I plan on trying both and don't expect to notice a difference, thus the question: which would you suggest to be the more appropriate capacitor to try?Thanks.

author: SeanB
author_rank: Super Contributor
timestamp: January 04, 2016, 09:20:13 am
content: Mylar film, you do not need the potted box here in an application running off under 10V. Generally a green or brown paint, and a lot cheaper as well.