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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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A *Big* question !
Primarily - what you look for when buying a scope depends on what you're going to do with it and for how long.
Think of it like a battery drill. If you are going to drill 10 holes this weekend, and then pop it in the shed until 9 months later, then a $25 bunnings cheapy will probably be fine and its less money to lose when you cant find the charger or discover the shed leaked on it 9 months later.
If you're a pro craftsman and are going to work your tools hard on a regular basis, then you spend some more and get stuff that is designed for hard regular use.
So with scopes, if you want to check a servo pulse, watch voltage ripple or other trivial functions like that once in a blue moon, then any el-cheapo laptop-usb scope with 1 channel and 10mhz will be fine.
If you are going to use it on a regular basis, then you will want *real* knobs and buttons.. not mouse-clicks.. think of it like an on-screen phone style keyboard or one that you click on with a mouse vs a real keyboard. to type the occasional message it might be ok, but not to write anything long. Buttons and Knobs are the same. Use it more than once a week and you will be glad you went for hardware and not software knobs.
If you expect to be able to dive into hacking brushless ESC's, designing FET bridges, or rolling your own custom microcontroller widgets, then you will want 20-50mhz bandwidth.. If you expect to be diving into high powered micro's or RF modulation stuff, then 100mhz + would be good (pricey though). If AVR/Pic/Arduino/Stamp micros are your plans, then 20mhz will cover it.
Logic/Spectrum Analysers are pretty advanced features. I cant see anyone who needs an "Introduction to Oscilloscopes Guide" needing anything like that any time soon.
Protocol Analysers (serial, USB, I2C, SPI etc) can be useful if you plan on going a bit deeper into Micro Land and want several widgets to be able to talk to each other without you having to guess what theyre saying between themselves.
Brand Names are for quality/reliability/accuracy/longevity. If you buy a hooflungdung co. scope or meter, dont count on it having a working life of more than a year or three.. you might get lucky, but then again you might not, and good luck finding them 5/10 years down the track. If its a semi-disposable scope (sub $500), then you might not care.
For Meters and other highly portable gear, toughness is what you want. Meters tend to get balanced on shelves, chucked in toolboxes, dropped into engine bays and all sorts of other abuse. a wimpy plastic one likely wont survive its first encounter with the floor. an imitation fluke-style plastic surround wont necessarily help much if its not designed well - it has to be good rubber, fit will, protect protrustions etc.
Accuracy ? Within 0.05v is close enough for hobbyist work. Certified Calibrations arent necessary unless youre doing aerospace/medical stuff or deep analog design.
Fancy functions ? 90% of measurements are voltage or resistance. another 5% are current. Everything else (cap, inductance, freq) are the last 5%. Thermocouple/Temp can be useful on occasion, but not often.
The most often used piece of gear (not "test gear through") is without doubt your Soldering Iron. Without it you cant do jack. The difference between "OK" and "Good" is huge. Dont Skimp on it. Get a Weller, Hakko, Micron or other brand that has been in the Biz for 10 years +. El Cheapo Brand Tips suck, oxidize quickly and evaporate leaving an awful surface. Result - Poor Joints full of crud, unpredictable heat transfer slowing down speed soldering and messy flux flows. Spend your $$ here first, Solder is the glue of electronics, if its not right, nothing will work.
After that, a Solder Sucker (got to be able to fix mistakes). If youre not going for a pricey power desoldering tool (electric vacuum pump), but for a hand model, there is only *1* name worth using. SoldaPullt. Stupid name I know, but ask any pro electronics person - Ive never heard anyone who has used one ever want anything else. Bonus Tip - Add a small length of ubernable pure silicon tube to the tip for a better flexy seal.
After that, its Meters, Scopes, Current Limited Adjustable Power Supplies. Bench Lights, Magnifying lens/lamp, small bench vise, tweezers (the self clamping type), Pin Drills, Wiring Pencil (an awesome recent addition to my toolbox), scalpel, the best damn quality sidecutters you can find. component draws, clipleads, pin files, crimps, auto-wire-strippers, breadboard, insulation tape, heatshrink, iso alcohol, soldering flux, a dremel & bits, etc etc..
Any more detail you would like ? _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Thu Jul 07, 2011 9:02 pm |
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Valen
Experienced Roboteer
Joined: 07 Jul 2004
Posts: 4436
Location: Sydney
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I'd suggest for getting into robots get 2 (or more) $10 multimeters.
There's not much advantage to fancier ones and we use them "in the field" a fair bit so they are likely to get broken. They are accurate enough for what we do. I have an autoranging one and i find the autorange somewhat a meh feature.
It takes it a while to cycle through the ranges and you need to double check the scale to see that it is infact 24 volts not a 24 milivolt leakage your seeing.
Also when somebody tries to measure how many amps their battery pack has they wont feel too cut when it catches fire. (or measure how many amps the spark plug in their car uses, that is funny to watch btw, the 300V insulation works just well enough that it breaks down only where the persons hands are holding it, make sure your not drinking any beverages when watching somebody try this, also it breaks the meter)
Audible continuity is a must, even if you need to get a $20 meter to get it, make sure you have at least one meter that does it.
I've never really used anything outside of volts amps and resistance measuring. I use a precision current shunt ($10 @ jaycar) to measure high or unknown currents, not as handy as a clamp meter but cheap and accurate also you can use them with a scope to look at what the current is doing in real time.
Also buy or make some leads with aligator clips on, (handy for establishing a ground) and "pin hook" type probes are handy too.
Moving up from there, there are a number of iphone sized scopes floating around with decent sample rates http://www.sparkfun.com/products/10244 to enter or http://www.sparkfun.com/products/10388 (i think you can get this or a similar device for ~$100) that'll do 72mega samples per second.
Either one would be good enough to look at servo signals and brushless stuff, though the slower one wouldn't see any ringing.
If your doing development there are a few open source logic analysers floating about that are high speed, lots of inputs and have a moderate buffer size, They plug into the PC and the pc software can do things like decode I2C/serial comms etc which can be really handy. There is a closed source one that's around $150 from memory and its software decodes pretty much everything as i recall.
For robots and general electronics, i'd put the logic analyser above the need for a scope unless you start playing with building ESC's.
That said, i don't have one, but its going to be my next purchase ;->
My general philosophy is buy a wide assortment of cheap crap tools, if you break one or wear it out, replace that thing with a good quality item because you know you use it, and you haven't spent $200 on a tool you hardly ever use.
Also check out ebay, you can get some really nice older gear for the same price as a new item except its a 700mhz TEK vs a new noname 100mhz scope.
I have a 700mhz 4 channel tek and its come in handy to see bastard power spikes in supply lines causing switch inputs to trip intermittently.
(oh those rigols you can get the cheap one and do some software hack to make them run *way* faster ;->) _________________ Mechanical engineers build weapons, civil engineers build targets
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Fri Jul 08, 2011 10:20 am |
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