- Diode On Small dc Toy Motor: Why ? - 5 Updates
- HP 339A Info - 2 Updates
- Charging gel cells in series - 1 Update
| Bob <rgsros@notme.invalid>: Aug 04 08:01AM -0400 Hi Folks, I'm not an EE, so would really appreciate someone educating me a bit on this. Trying to fix kids toy. Very simple electrically, just a battery going to one of those small, cheap, probably a PM type, dc motor that does nothing but spin a pointer. For some reason, they have a diode in one of the leads to the motor. (in series with one of the leads) The Diode must be defective, for if I by-pass it, the motor spins just fine. Can't imagine why the Diode. Hard to believe that it is for any RF suppression due to the brushes that are apparently on this really small dc motor ? Anyone have any thoughts perhaps as to for what purpose the diode was included ? Thanks, Bob |
| Baron <baron@linuxmaniac.net>: Aug 04 01:43PM +0100 Bob prodded the keyboard with: > was included ? > Thanks, > Bob To ensure that the motor spins in the right direction and not to spin at all if the battery is reversed. -- Best Regards: Baron. |
| N_Cook <diverse@tcp.co.uk>: Aug 04 02:01PM +0100 On 04/08/2015 13:01, Bob wrote: > was included ? > Thanks, > Bob There seems to be a few types of small diode constructions that are guaranteed to fail an overcurrent by going open circuit. Cheaper than a wire-ended fuse , and as a plus, battery reversal protection |
| Phil Allison <pallison49@gmail.com>: Aug 04 06:23AM -0700 Bob wrote: > Very simple electrically, just a battery going to one of those > small, cheap, probably a PM type, dc motor that does nothing but spin a > pointer. ** I guess the " pointer" does not spin at the same rpm as the motor, cos there is a gearbox ? > For some reason, they have a diode in one of the leads to the motor. ** You are sure it is a diode because ? > The Diode must be defective, for if I by-pass it, the motor spins just fine. ** What if you reverse the cell in the holder ? > Anyone have any thoughts perhaps as to for what purpose the diode > was included ? ** I have a possible theory in mind, but you need to describe the gadget a lot better. ... Phil |
| M Philbrook <jamie_ka1lpa@charter.net>: Aug 04 12:22PM -0400 In article <mpq9hf$1cg$1@dont-email.me>, rgsros@notme.invalid says... > was included ? > Thanks, > Bob My guess would be maybe to prevent charging of the power source? That would happen if you hand spin the pointer. But it could also be suppressing noise by not allowing current to flow on EMF back voltages. Jamie |
| jurb6006@gmail.com: Aug 03 03:07PM -0700 Now I notice the onboard oscillator goes up to 110 KHz. Also, I notice that the bandwidth is only 110 KHz. This should mean that it really cannot measure any distortion on the 110 KHz from the oscillator. At 55 KHz it would only pick up the second harmonic which is pretty much useless. Now that the thing seems to be acting right, when it comes back it will be time to see about accuracy. It actually belongs to my partner but we kinda don't care who has what as long as we got the basics. He has frequency counters, and this. I have everything else. He lacks a really good function generator, well he decided to tinker with it. There's another story that might warrant a thread. I did a workaround that made it work almost perfectly but this guy is a fanatic about measurement and things like that. I can start the thread but any real working on it will have to wait until I figure out what went wrong. I think he has some wires connected wrong. They are all individual with almost no markings, though some of them have a little paint on them. Few. So basically this thing will be back. It was here a few days. Probably in a couple of weeks after he tinkers with it. Anyway, it is good to know that I can check this thing. If the readings are within reason I should be able to trust it enough for the kind of audio I do. See I will work on high end and vintage stuff, but I do repairs, not restores. I don't go changing every capacitor in a unit with those high resolution types. I have tried to explain that to some people and some understand yet others claim thy can hear the difference. The way I see it is if you can hear it I should be able to measure it. In fact that claim was made and proven by Bob Carver. He, in one act (well a series of the same) not only proved that the regular IHF specs don't tell the whole story, but also put some of the audiophoolery to rest. It IS measurable, and what I say is that if it IS measurable then what is not measurable should not be hearable. Then it gets to the realm of psychoacoustics. Then it also gets to the point where people might WANT some distortion. Electric guitarists are certainly not afraid of distortion. Anyway, back to this. Since it is a notch filter based device we know it is measuring THD + noise. Anything outside of the notch counts. I have contemplated a way to measure that without such a device. (yeah, now we got one and won't need it HA !) I have, in the past, taken and nulled out the input and output of an amp using the add function on the scope, and usually having to invert one channel. The scope will display THD+N but will also indicate if there is any phase shift. You start getting up near the upper limit in frequencies, many audio amps have considerable phase shift. To solve that, first of all I do not want to tamper with the signal coming back. But the sine wave going in, where it goes either to the DUT or the scope, I could shift the phase around a little with a cap and resistor. Bottom line, in an amp the phase is going to lag of course. So all I have to do is lag it a little bit where it goes into the scope or whatevr actually does the nulling oin this case. That still leaves the problem of deriving an RMS measurement out if it which means nulling it externally and using a true RMS meter. I have a Fluke down there. I just checked and it says it is down -3 dB at 200 KHz. So I can use the scope to get the best null in both aplitude and phase with a pot and a cap, and then what the Fluke sees on there in RMS should be comparable to the total amplitude and then we can derive percentage easily. In fact using the KISS theory just keep it at like 10 volts RMS or something that makes it easy to divide. (when possible of course) Make it read 10 on the Fluke and then switch the source to the nulled signal. Now this is nulled electronically, not with a tuned circuit. Except for the notch filter, that 339A is just a generator and an oscillator. Question is how hard will it be to get a comparable accuracy as opposed to something like the 339A ? One thing about it is that any distortion in the source oscillator is also nulled and is taken out of the picture. This should lower my measurement floor if it works. Another question, should you decide to field, and able, is what about PURE THD ? I mean pure THD without the noise. The only way I can figure is to exploit the randomness of the noise by somehow recording the output and synching it somehow to get an average reading from a number of cycles. The problem with that is the only real way to do it is digitally or BBD. If I want a low measurement floor there, that is going to have to be one hell of a BBD. But is there another way ? They routinely say THD, not THD+noise. Either there is a way to null out the noise, or they are using signal levels that make the noise insignificant. I don't see how this would be easy on something like a moving coil phono preamp. Very few, but some of them are complimentary push pull and in those you might want THD measurements at the lower levels. In the ones that just use single ended stages not so much. Mostly you would want to use higher levels anyway because the THD levels will be higher then. It is just that it is not true of the fully complimentary ones. Sorry this is getting so damn in depth but I guess that's the way the rock rolls. |
| Phil Allison <pallison49@gmail.com>: Aug 03 07:51PM -0700 > The only way I can figure is to exploit the randomness of > the noise by somehow recording the output and synching it > somehow to get an average reading from a number of cycles. ** Digital scopes can do that job, by averaging a number of screens. When the scope is synched to the test frequency (using ext trig), it is also synched to the harmonics. So averaging 8 or 16 screens removes much of the random noise and hum. ... Phil |
| mike <ham789@netzero.net>: Aug 03 12:36PM -0700 On 8/3/2015 4:16 AM, pedro wrote: > parallel charging - well, floating actually - is what is required. > Refer to the cell manufacturer for the appropriate voltage and do as > Tom Miller suggested. Charge 'em in parallel, except put an incandescent light in series with each so the current can't be hogged by one. Some "smart" chargers might object to that, but a dumb float charger should work just fine. I'd suggest that, if your need is so infrequent such that you need to recharge 'em, you're stocking too many replacements. Find a high-turnover supplier with short delivery time and stock fewer batteries. Fresher is better. |
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