Hello to all - and some trivial questions that drive me crazy... - Page 1
Forum section: electronics / beginners

author: grueni
author_rank: Newbie
timestamp: September 20, 2015, 12:34:20 pm
content: Hi !Hello to all!About me:I'm interested in electronics - but quite a noob.I watched many of Daves episodes... I both love and hate them. Love, because they are great, comprehensive, interesting, ... Hate, because I now spend way to much time on electronics :-DI'm not in many forums, I haven't been speaking or writing english for about 3 decades - so please forgive me my horrible english.Sorry, I really hate to ask newbie-questions in a pro-Forum... But I hope you don't mad at me.Tough they are trivial - I swear I tried to solve them... But I couldn't :-(Maybe there would be a chance for some new "fundamental fridays"-episodes..I didn't want to start up with many different threads - so I put all my first questions in this thread. I hope, this is allowed.1.) Transistors:For a simple circuit, I decided to buy some BC327-40.When I look for them in a shop, e.g.https://www.conrad.at/de/search.html?search=bc327-40I see many of them.For example there is a BC327-40BK, that has a different price tag than the BC327-40 ... But as far as I know, both have the same datasheet.So question number 1: What are the differences here?My next question is also on the bc32x :In my design, a bc328 would also suffice...As much as I found out (looking in the datasheets), the bc328 has all the same values as the bc327... The only difference is that the bc328 has a Uceo of 25V, and the bc327 has a Uceo of 45V .... And the bc328 is more expensive.So my question number 2: Is there any use case where you pay extra for a device with less Uceo? Using a transistor like a fuse?? Or do I miss something?My question number 3 would be a feature request for a "fundamentals friday": I want to use transistors to multiplex 7-segment-displays. When reading about this, you sometimes read that there is something like a "miller-capacity" in transistors that could bite you... Maybe Dave could do a video on how to avoid (or how to use) it :-D2.) LDR:I want to measure environmental light to adapt the brightness of a 7-segment-display. My idea would be to use the LDR as a resistor for loading a capacitor... and to measure the time from "c is empty" to "the voltage on C reads high on a pin of my µC"....So question number 4 would be: Is it okay to use an LDR like this? Or should I use the ADC of a µC ? Are there different ways? Are there some things to look at? Is there e.g. something like a maximum frequency you are allowed to use your LDR?3.) Multimeter Reviews:Dave explained once in a Video, that he tests all Multimeters by putting them on the ohms range and connecting them to the mains.Question 5: Does he also try this with the bench multimeters?Bench vs. handheld multimeters: In earlier videos, Dave explained that bench multimeters barely make sense.. And that it would be better to buy handheld multimeters. But when he tested bench multimeters, he looked quite excited.So question 6: Did I get the first point wrong or are bench multimeters quite nice?The next 2 questions are ones where I really want to understand the "why":When we look at a typical DSO for hobbyists: Lets say they can measure down to 2mV per DIV maany times a second...Why don't do they have a mutimeter-functionality too? I mean, yes, they do have only 8 bits resolution - but most of the time, I'd be quite happy with that. Or could it be that I'm the only one that would sometimes prefer a simple, good readable Digit-view of Volts on a DSO?Question 7: Why don't DSO have a multimeter-functionality?Multimeter vs. µCurrent:As much as I get it, the µCurrent could be used as a "Voltage x100"-device... and as an instrument to read exact low currents. My trivial question 8 is: Why is this circuit not integrated in better multimeters or oscilloscopes? Are there drawbacks that I am missing?Question 9 and my last one for today:Maybe I'm really that stupid, but I can't understandhttps://eevblog.myshopify.com/products/ucurrentquestion 9: Is it possible to order from Austria?

author: radioFlash
author_rank: Regular Contributor
timestamp: September 20, 2015, 04:37:19 pm
content: * The difference between the BC327-40 and the BC327-40BK seems to be that the BK variant has straight leads and doesn't come on tape, while non-BK version has kinked leads and comes on tape.http://diotec.com/tl_files/diotec/files/pdf/datasheets/bc327.pdfhttp://diotec.com/tl_files/diotec/files/pdf/datasheets/bc327bk.pdf* Bench multimeters--this is a matter of personal preference and what you're working on. In my case, I find it easier to use a bench multimeter because it doesn't get lost somewhere and I don't have to worry about changing batteries on it. It's also nice to have the logging capability and the higher precision / accuracy. However, if you're just starting out and only have one multimeter, it's probably best to start with a handheld.

author: codeboy2k
author_rank: Super Contributor
timestamp: September 20, 2015, 05:08:12 pm
content: Hello and welcome.1. The BK suffix signifies BULK packaging. It means you get loose transistors in a bag if you buy those. The other transistor would be on a tape, sticking out one side and the tape has holes for the feeder. This is called AMMO pack.2. Pricing fluctuates and can depend on availability, popularity, or the phase of the moon. Buy what works for your circuit when you need it to work3. Good idea for fundamental fridays, re: the Miller Effect. For your particular example, multiplexing 7-segment displays, you will not be affected by the Miller Effect, because multiplexing is going to be fairly slpw (120Hz, 400Hz, etc). This is too low for the Miller Efect to really be seen. It is basically an increase in input capacitance of a circuit (i.e. the capacitance as seen at the input to a transistor amplifier) at high speeds, which can limit the high-frequency response. It won't be an issue for multiplexing a 7-segment display.4. your idea is interesting, but you can't really rely on the exact input voltage that will appear to be a '1' at the input port of a microcontroller. So you don't really have too much control, and there will be wide variations from each part, and maybe even from the same part. It can work for a simply binary case, i.e. it's dark / it's light.. and then you choose your charging current and capacitor such that there is a wide enough time between one and the other such that you can reliably count the charge time and discern the two states, despite the variations in timing that you will see.5. I can't remember which video, but yes, I've seen him test bench meters by putting mains on the ohms ranges too.6. I prefer bench meters on the bench. I hate the time-outs on handhelds, and the constant need for batteries. You need both types in my opinion, since you will want to bring a meter to your circuit sometimes.7. Most scopes these days do have voltage displays, but aren't really hardware based voltmeters. They usually just use the sampled data points to calculate this. It's done this way because a hardware voltmeter in the scope is less useful, since you almost always want more information, such as peak, peak-to-peak, average, std deviations, or cursors. This is easier done by using the sampled data instead of using a separate hardware voltmeter built in. And scopes don't need resistance or current measurement, so it's not ever going to be a "multimeter". Scopes can "measure" current when told that you have a current probe hooked up; then it can provide all the same measurements that it would for voltage, but scaled for your current probe.8. Most don't simply due to cost; manufacturers don't want to put extra bells and whistles, and meters have always been designed to measure the things that were most likely to be measured. However, with more and more low voltage, low power and battery operated devices, it makes more sense now to have a multimeter with better low-voltage and low-current capabilities. I expect that manufacturers will start adding better low current ranges with lower burden voltages, simply because today's microcontrollers require it.9) The uCurrent is available from Simon (SparkyLabs). Checkhttps://www.eevblog.com/forum/chat/ucurrent-now-available-in-the-eu/

author: helius
author_rank: Super Contributor
timestamp: September 20, 2015, 05:08:51 pm
content: Quote from: grueni on September 20, 2015, 12:34:20 pmDMMs are most often used in combination with other instruments, so using a scope as a DMM is awkward. The 10M? input impedance is also low for a voltmeter and not the greatest way to measure voltage in a circuit. To see the voltage the way a DMM would you need to turn on averaging.Scopes once came with DMMs bolted on, as in the Tektronix 465/DM44 option. But this takes up valuable space for a feature that was never especially great.

author: drws
author_rank: Unknown
timestamp: September 20, 2015, 05:28:15 pm
content: I thought w2aew's Miller Effect video was very good:https://youtu.be/Op_I3Ke7px0Might be useful to you.

author: grueni
author_rank: Newbie
timestamp: September 21, 2015, 04:59:47 am
content: Thaaaaanks for all the answers!It's great to see them coming up fast and competent - Thanks again!So to put a long story short:1.) @parts: BK means "bulk" - thanks!2.) @transistor as fuse: Nope. Prices just don't correlate with features.3.) @miller capacity: Thanks for the Video! I'll watch it after work!4.) FOLLOW UP-Question @LDR and measuring time: This one is a little bit open. I don't need a full readout of lux... I just want to have 8 or 16 steps going from "No light" (10 MOhms in my case) to "veeery much light" (20 Ohms or so). Because of the wide range, I thought measuring time by loading a cap would be easier than using an ADC... So when I get it right, it should be possible measuring time... But either way, I need a calibration because of very different part behaviour?5.) FOLLOW UP-Question on bench multimeters and the Ohms range: When using Oscilloscopes, I have to take care when measuring circuits on mains... (I really loved Daves "How NOT to blow up your oscilloscope" :-D. ) - because the probe is connected to GND of mains. How about bench multimeters? Are they floating, or do I have take care like when using an oscilloscope?6.) @bench multimeters: Ok, they are practicable.7.) DSO as Multimeter: I would love if my scope could sometimes just display the Volts with _big_ letters... plus some statistics like average/min/max Volts in the last, last 5 and last 15 mins... My point is that you wouldn't need extra Hardware - it should be all possible in Software But it looks like everybody prefers different devices - so nowbody implements it in scopes...8.) µCurrent integrated in multimeters: Let's see, if they are coming. In my case, I love playing around with pics. The 12F675 has a standby current of 1nA... I'd love to see if I did everything right in my circuits - so I'd love to measure with a resolution of ½nA -> 500pA. I couldn't find an affordable multimeter to look at this range... Most stop at 10nA resolution.9.) FOLLOW-UP-Question ordering µCurrents: What does the list on the bottom mean? Is he only shipping to these countries? (yeah, I found his message on sparky labs - but I'd like to know if it's cheaper ordering from him :-D )New Question / Feature Request:In all the PICs I know of, there is a comparator included... I believe I did some circuits way to complicated, because I didn't use ist. So it would be nice to see a fundamentals friday on comparators: How to use them, differences to an opamp, ... -> Does someone have any good videos on this topic at hand?

author: codeboy2k
author_rank: Super Contributor
timestamp: September 21, 2015, 10:39:23 am
content: 4) measuring the cap charging time is essentially what one type of ADC is doing, so if you build a circuit with your LDR and use that and a constant current to charge a cap and use a timer to time how long it takes to flip an input port's bit to '1', then you've just made yourself a rudimentary ADC. The input port will have some hysteresis and the actual voltage at which it changes state can vary from part to part, so that is where you might have some trouble with this approach. However, you said you only want 8 or 16 steps and this corresponds to 3 to 4 bits so it might be possible.Note that an LDR is non-linear, so you can't do a simple calibration at the extremes by taking two timings at the light and dark ends and dividing this by the number of steps you want. You'll need to make a voltage divider out of the LDR and another bottom resistor, and furthermore parallel the LDR with a lower value resistor to try to linearize it somewhat. Then use that to time the charging of your capacitor.Frankly, I think it's overly complicated for you to do it this way. You're not really saving anything, and making more design work+calibration and you have a higher component count. You would be much better off just using the LDR and a bottom resistor as a voltage divider input directly to an ADC pin on the microcontroller, and then linearize the curve entirely in software with a table lookup or a few control points and a formula.5) Bench DMM's are floating, yes.9) I'm not in the EU so I don't know, so you'll have to ask Simon about the specifics of the uCurrent from him. I think there were many EU customers seeing delays and added taxes and duties when importing from Australia directly, so Simon has inventory and can ship directly from within the EU, so you have the possibility of avoiding import delays and saving money by not paying excessive import taxes. So contact Simon directly and see what he says.Cheers!