Hi,
I'm looking to get an oscilloscope. Problem is that I haven't got a clue how to interpret the specs. Most important of that being the sample rate. I don't know how the scope sample rate relates to the stuff you want to see. The most important thing I need it for is engine management research. Meaning for a four cylinder engine @ 15k rpm, about 500 ignitions per second. Will a 40MHz scope suffice to do stuff like this?
Best regards,
Sylvain Girard
Generally, I'd look for a bandwidth of five to ten times the maximum frequency you would expect to measure.
15 000 rpm is only 250Hz, so even a 5 or 10MHz scope would be adequate.
However, if you can afford it, go higher and you won't need to buy another for some time.
AWOL:
However, if you can afford it, go higher and you won't need to buy another for some time.
Sylvain's question seems to indicate a lack of experience using a scope; his time period for buying another may be much shorter than your's or mine...
Sylvain - I would first buy the cheapest scope you can find - something like:
http://www.jyetech.com/Products/LcdScope/e062C.php
Which, IIRC, only costs around $50.00 USD...
Then find yourself a source of signals (JYE also sells function generators - but anything cheap that uses a 555 will do) for square, sine, and triangle waves, sit down with a tutorial, and learn how to use that scope. Once you are really comfortable with it, then spend the money buying a more expensive scope. The last thing you want to do is spend several hundred dollars on a new scope, only to overdrive it and burn it out (easily done if you don't know what you're doing - and sometimes, even if you do).
You can buy incredibly cheap PC oscilloscopes (i.e. ones that run from a laptop usb port and use the laptop for the display and controls) from China/Hong Kong on eBay. For example, this one http://www.ebay.co.uk/itm/2-Channel-PC-Computer-USB-Digital-Storage-Oscilloscope-/290550560370?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item43a629b672 is only GBP21 including carriage (but only spec'd up to 3kHz), while this one http://www.ebay.co.uk/itm/DSO-2090-100Msa-s-USB-PC-Virtual-Storage-Oscilloscope-/320467863941?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item4a9d5f8985 is spec'd up to 40MHz and costs GBP109. I haven't any experience of these so I don't know if they are any good, but I'm tempted to buy one.
There's even an Arduinoscope sketch to turn an Arduino into a low-frequency PC oscillosope.
dc42:
You can buy incredibly cheap PC oscilloscopes (i.e. ones that run from a laptop usb port and use the laptop for the display and controls) from China/Hong Kong on eBay. For example, this one http://www.ebay.co.uk/itm/2-Channel-PC-Computer-USB-Digital-Storage-Oscilloscope-/290550560370?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item43a629b672 is only GBP21 including carriage (but only spec'd up to 3kHz), while this one http://www.ebay.co.uk/itm/DSO-2090-100Msa-s-USB-PC-Virtual-Storage-Oscilloscope-/320467863941?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item4a9d5f8985 is spec'd up to 40MHz and costs GBP109. I haven't any experience of these so I don't know if they are any good, but I'm tempted to buy one.There's even an Arduinoscope sketch to turn an Arduino into a low-frequency PC oscillosope.
While attractively priced, they both seem have a maximum 5 volts input specification. While that is useful for logic and low level stuff, I would find that limit would cramp my style. Guess I'll just stay with my vintage analog Tektronix 2213 scope. 
I've been thinking about picking up this 404 - Page not Found one. -14V to 20V in, only goes up to 200Khz :(, but it has a built in protocol sniffer and some other nice features. Only $50.
retrolefty:
While attractively priced, they both seem have a maximum 5 volts input specification. While that is useful for logic and low level stuff, I would find that limit would cramp my style. Guess I'll just stay with my vintage analog Tektronix 2213 scope.
Presumably 50v with a 10x probe - but if you already have a Tektronix, I guess you've no reason to look elsewhere!
I got a nice analog oscilloscope (dual channel 60MHz) on Ebay for only about $100, after giving up on finding a USB plugin that would work on a Mac OS X system.
The problem with analogue scopes is that they generally don't have any storage capabilities.
Great for repetitive waveforms, not great for catching one-offs.
I started with analog... and then realised I wanted more...so replaced it with a lecroy waveace.
FWIW, I recently replaced my well-worn 70s vintage Tektronix 475A with a Rigol DS1052E; it's a nice little digital scope, seems to get decent reviews, and is aggressively priced given its feature set. Got mine through saelig.com in the US, free shipping plus three year warranty.