Trap for young players? - Page 1
Forum section: electronics / general

author: KTP
author_rank: Frequent Contributor
timestamp: August 08, 2012, 11:09:21 pm
content: There is this thread on the Agilent forum from a user who was only getting .3Vpp out of his new DSOX2012 when he set the WFG for 5Vpp. I read it a few weeks ago and thought bummer, he got a bad unit. Today he posted a pic of his setup, using 10x probes (this was with a new scope after he sent the old one in for replacement)Original thread here:http://www.home.agilent.com/owc_discussions/thread.jspa?threadID=33503&tstart=0

author: kg4arn
author_rank: Unknown
timestamp: August 08, 2012, 11:46:54 pm
content: I saw this today as well.Read the responses from Al and Kevin, the Agilent engineers.Agilent has been just as patient (and kind) when I have needed their help as well.

author: David_AVD
author_rank: Super Contributor
timestamp: August 08, 2012, 11:51:28 pm
content: The referenced thread says that using 2 x 10:1 probes (one on output and one on input) will give you a 20:1 ratio. Hmmm... even if it was 2 lots of 10:1 in series, that would be 100:1 (10 x 10).The 10:1 probe on the input would give a 10:1 reduction, but a 10:1 probe used backwards (on an output) would not.The output would see the shunt resistance and there would be a series resistance making the signal at the probe tip some higher impedance. That coupled with the input probe's input series resistance would alter the 10:1 reduction as well.So two 10:1 probes used (incorrectly) like that could yield some odd results!

author: Bored@Work
author_rank: Super Contributor
timestamp: August 09, 2012, 05:06:42 am
content: Sorry, this is not a trap for the young player. This is a trap for someone who bought an oscilloscope + wavengen (maybe "because Dave said so ...."), without having a clue what he is buying and what he is doing.Even just a multimeter, least an oscilloscope, is not a consumer device, and investing some time to learn at least the basics is rather advisable when buying a such stuff.

author: northlondonsage
author_rank: Contributor
timestamp: August 09, 2012, 08:24:13 am
content: Bored@Work:A pro in any field who lacks patience with beginners is suspect.

author: ftransform
author_rank: Frequent Contributor
timestamp: August 09, 2012, 08:31:45 am
content: someone needs to have a nice relaxing glass of camomile tea.

author: David_AVD
author_rank: Super Contributor
timestamp: August 09, 2012, 10:41:48 am
content: I do agree that the referenced thread showed a basic lack of understanding. It seems like there are a lot more people these days buying equipment (that requires a fair understanding) before they have the slightest grip on electronics theory.Maybe it's considered boring or menial (by some beginners) to learn Ohms Law before advancing to higher level principles?

author: Omicron
author_rank: Regular Contributor
timestamp: August 09, 2012, 11:51:30 am
content: Quote from: David_AVD on August 08, 2012, 11:51:28 pmNope, the reply of the Agilent guy is perfectly correct. A 10:1 probe is basically just a resistor that forms a divider in combination with the input resistance of the scope (well in reality it also has a capacitive divider in parallel but that doesn't really matter for this discussion). Putting 2 probes in series just doubles the resistance of one leg of the divider giving you (approximately) 20:1. Doesn't matter one bit if one of them is "backwards".Perhaps a review of ohm's law is in order?

author: David_AVD
author_rank: Super Contributor
timestamp: August 09, 2012, 12:01:29 pm
content: Hmmm... there's a gap in my knowledge of scope probes it seems! Happy to be proven wrong!EDIT:Just thinking about it some more. The two probes (in series) would end up giving you a 19:1 ratio (1M + 2x9M: 1M). Even old farts like me can learn new stuff.

author: KTP
author_rank: Frequent Contributor
timestamp: August 09, 2012, 01:05:01 pm
content: Quote from: David_AVD on August 09, 2012, 12:01:29 pmActually it is only 2x9M: 1M which is 18M in parallel with the 1M input resistance...which is still 19:1 ratio as you said.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: August 09, 2012, 01:41:02 pm
content: The ratio of the resistances is 18:1 (2*9:1) but the signal is attenuated by 1M/(1M+18M) = 1/19. This is under the assumption that a probe contains only 9M resistor, meant to create a resistor divider together with the 1M input impedance.

author: northlondonsage
author_rank: Contributor
timestamp: August 09, 2012, 01:50:40 pm
content: David_AVDHave you seen this? High level language players whether young or old can implement microcontroller plug-and-play circuits without knowing Ohms Law, or in fact anything. To get a led to flash when you push a button will cost you about $100 though. Rapid prototyping they call it.http://www.seeedstudio.com/depot/gadgeteer-c-203.htmlI'd love to see Dave take a look at this stuff...

author: David_AVD
author_rank: Super Contributor
timestamp: August 09, 2012, 10:03:40 pm
content: Quote from: northlondonsage on August 09, 2012, 01:50:40 pmI have mixed feelings about stuff like that.It's good that people can learn to program without having to worry if the hardware they put together is even correct. If you're going to use the same (pre-built) hardware for the final version and it does the intended job, you can move onto the next project.On the other hand, if the rapid prototype platform can't be transferred to the required custom board later, then the lack of "nuts and bolts" knowledge can cause a lot of grief.I guess it comes down to the application. If the object is to learn programming and you're not really interested in hardware design, the Arduino type of board is probably the right fit. If you want to make something in a form factor that the pre-built solutions don't provide, you really do need to learn about what makes things tick at a lower level.I myself program most of my PIC projects in assembler and do custom boards all the time. I also program in Basic (Cubloc touch screens), C (Moacon controllers) as well as Delphi (PC apps) and even the odd bit of php and html (for web apps). I can see myself using C more on the PIC projects in the future though.Sometimes I like making my own boards even when there are pre-built options available. Circuit design and PCB layout can be quite challenging and I enjoy that aspect of it. (I must do as I'm fast approaching PCB design # 800 !) Others just want to make that LED flash or relay click and only want to deal with the higher level aspects. That's fine too. Different strokes and all that.

author: David_AVD
author_rank: Super Contributor
timestamp: August 09, 2012, 10:12:57 pm
content: Quote from: KTP on August 09, 2012, 01:05:01 pmSorry, I should have said that it's an 18:1 resistive divider that results in a 19:1 voltage ratio. I was just showing that the 1M is actually present on both sides of the voltage equation.

author: free_electron
author_rank: Super Contributor
timestamp: August 09, 2012, 10:47:07 pm
content: I'm trying to imagine what a smartphone or TV will look like when it will be designed by the generation of people that grew up with arduino or those gadgeteer style blocks. it'll be about 3 feed by 2 and a foot tall , come with a 15 mile extention cord and the display will be made with blinking led's...i've got nothing against such 'toys'. in fact i frequently use such pre-built little boards if i need to test out a concept , but in the end i do design my own circuit board and it goes in a custom enclosure.sadly that is something the arduino generation does not do. they are stuck to a contraption with 3 shields and a wire-spaghetti.RAD systems are very useful to test out a concept. but you have to move on after the concept has been proven.Anyone showing off an arduino contraption as a final product gets it widlarized. I keep a box of hammers around for just such instances. Special red toolbox labeled 'widlarization toolkit'

author: slateraptor
author_rank: Frequent Contributor
timestamp: August 09, 2012, 10:50:55 pm
content: Quote from: northlondonsage on August 09, 2012, 08:24:13 amBlatant failure to RTFM hasn't earned the grace of patience.

author: northlondonsage
author_rank: Contributor
timestamp: August 10, 2012, 07:34:16 am
content: "Blatant failure to RTFM hasn't earned the grace of patience."Nonsense. You have to look after the young players...We all got stuck on stupid things when we were starting out. My idiot questions and yours, no doubt, were asked in private labs and are long since forgotten. Some kindly lab tech would explain Ohm's law yet again and to him, RTFM was a friendly joke, not an insult I kind of admire the courage of those who are learning on the web and on the record. Glad I didn't have to.

author: northlondonsage
author_rank: Contributor
timestamp: August 10, 2012, 08:01:59 am
content: I think there is a difference, though between Arduino and .net gadgeteer.Most arduino projects, once working are obviously begging for their creator to design them a board and the parts are cheap and easy. Most arduino users are going to at least learn how to plug in a LED and a resistor, sensors, possibly even an H bridge and a MOSFET. They will have to get to grips with PWM and gain at least an understanding of voltage levels, ADC/DAC, breadboarding, not blowing stuff up, maybe even serial comms. It's most likely going to be used by beginners and hobbyists. Even using different shields involves thinking about pinouts. It's a good practical starting point.If you want to light an LED in .net gadgeteer, you buy a breakout board and set the brightness property in C#. The concept of PWM is hidden from you. You could use it without knowing even the name of the microcontroller running your code. It actually makes a virtue out of hiding the EE from the user. "Rapid Prototyping" seems to mean "not having to learn any electronics", and there is no real way of converting a prototype into anything more permanent.Anyway, I seem to be ranting a long way off topic.

author: kg4arn
author_rank: Unknown
timestamp: August 10, 2012, 10:27:35 pm
content: Quote from: northlondonsage on August 10, 2012, 07:34:16 amI'm with northlodonsage.Some observations...-As unusual as the test set up first appears, how many people must have looked at it and wondered to themselves: "Why shouldn't it work?" I know I did. And it wasn't until I drew the schematic out that I could see the 19:1 voltage divider and I understod why it worked at all.-At least one person (on this thread) admits to have a better understanding of the passive-resistive scope probe now. I know he is not alone.I hope the chap joins the EEVblog forums. I was going to suggest it to him but I was waiting to see if this thread would be overly unkind.

author: KTP
author_rank: Frequent Contributor
timestamp: August 10, 2012, 11:06:52 pm
content: Quote from: kg4arn on August 10, 2012, 10:27:35 pmThey are just upset because an obvious newbie got a crackin good oscilloscope as a starter (the Agilent x series), instead of having to start with a 5Mhz heathkit analog as they probably did.It is like giving a 16 year old a Bugatti as their first car instead of starting them on a Vauxhall.I didn't start the thread to be mean to the OP in that thread...I just thought it was amusing that the scope was sent back for repair because it failed to generate 5Vpp through a 19:1 divider heh heh. Poor scope.

author: David_AVD
author_rank: Super Contributor
timestamp: August 10, 2012, 11:19:26 pm
content: Quote from: kg4arn on August 10, 2012, 10:27:35 pmHehehe... I'm not unhappy when someone calls me out on something and I'm wrong.I've been into electronics for over 35 years and there's always something to learn. That's a fantastic thing in my book.What does bug me is the "I know everything about electronics" attitude that appears sometimes. TheDunning-Kruger effectis so on the money some days.