Test Equipment: Oscillocopes

[Pirate88179]

@MarkE: Thank you for starting this topic. I hope to learn a lot from it, and may be able to contribute a thing or two myself.




@Pirate: If you're a fan of classic analog equipment...

http://www.ebay.com/itm/Interstate-Electronics-Corporation-F-34-Function-Generator-115v-230v-/271740054768

That looks cool....thanks.  I love classic equipment.

Bill

[TinselKoala]

I have some books on C++ somewhere. Never did get around to learning it, though. I guess I have some motivation now.  What add-on board do you think I should get first, besides an LCD or a touch screen?

Depends on what you intend to do. There are literally hundreds of "shields" out there. The first "shield" that I got was the RuggedCircuits "Gadget Shield" just to play around with; it has 3-axis accelerometer, IR detector, IR emitter, RGB high-brightness LED, 2 potentiometers, 2 pushbuttons, 4 LED's, visible light sensor. The demo sketch for this one does things like have the RGB LED driven by the accelerometer, so it changes color as you tilt the thing around, etc.  I also have their "Aussie shield" which is just a "breakout" board with easy quick-connectors for external wiring. For the LCD, I have a Parallax branded thing that has a backlight and a little piezo speaker, that is part of the Parallax Propeller system, it uses just a single data line (serial interface) and the two power leads so you don't tie up lots of the Arduino output pins driving a raw LCD. I also have another LCD shield that has buttons but it uses the regular interface so it uses up 7 outputs IIRC. I don't have any experience with touchscreens so I can't recommend one. I've got a motor driver shield with high-output H-bridge motor driver chips on it for robotics stuff, rc servos and steppermotors. Also a prototype shield that has pads to build your own circuits on, I put a high power mosfet switch circuit on this one.

There are even signal generator shields and video displays that you can get for the silly things, probably even full oscilloscope shields.

http://playground.arduino.cc/Main/SimilarBoards  (lists many hardware items, shields etc with functional descriptions)
http://shieldlist.org/  (listed by manufacturer not type, unfortunately)

If you already have some programming experience but just not with c, or even if you don't, probably the best way to learn is just to look at example sketches and start changing them and see what happens. It's really pretty easy to do the basic stuff, the Arduino IDE comes with a lot of basic example sketches. Most people start with the "blink" sketch which just blinks an LED.  The Arduino online references are excellent and the programming interface is portable, runs on any computer OS, so you can write your sketches on a Mac, load them with Linux, run and display serial data on Windoze etc.

Here's a handy thing I made: 
http://www.youtube.com/watch?v=S6N8ys8FiA4

And just to steer back to the topic of oscilloscopes, here's a scoposcopy video showing how the Inductometer does its magic:
http://www.youtube.com/watch?v=Qx3B89379eQ

[TinselKoala]

That looks cool....thanks.  I love classic equipment.

Bill

It's kind of limited in that it only goes to 3MHz and has a low output level, but it's very versatile in its trigger/gating functions and it has the external VCO input so you can control it from an external variable voltage source. I have one of these in storage in Canada that I paid a lot more money for than the selling price here. My regular workhorse is another Interstate FG, the F43 model "High Voltage" FG, it doesn't do sweep but it has 40 v p-p into 50 Ohms output.

It is handy to have a higher voltage output level as well as a higher frequency range, so the more modern ones MarkE found on EBay are worth a look too.

[John.K1]

My question is than what setup (1x,10x...) to use when. Currently I have my probes permanently set to 10x.  Any general rule?
Next question - would it make sense to use de-coupling 1pf capacitor - sometimes I do use 1pF 5% 1KV  - but to be honest I do not see much difference on the screen when using it.
I am planning to buy 100x probe. - yes/no? suggestions?

TK, you was talking about integration MATH function, what is that good for?

50Hz modulation from the main- is it big issue?  any chance to filter it out?

Thanks.

[MarkE]

My question is than what setup (1x,10x...) to use when. Currently I have my probes permanently set to 10x.  Any general rule?
Next question - would it make sense to use de-coupling 1pf capacitor - sometimes I do use 1pF 5% 1KV  - but to be honest I do not see much difference on the screen when using it.
I am planning to buy 100x probe. - yes/no? suggestions?

TK, you was talking about integration MATH function, what is that good for?

50Hz modulation from the main- is it big issue?  any chance to filter it out?

Thanks.

Use 10X almost exclusively.  The only time 1X is useful is for low-level signals.  10X always offers equal or better fidelity and less loading on the circuit being tested.

Filters can be useful, there are several ways to go about them.  Most scopes have a 20MHz bandwidht limiting option on the front panel. From a noise standpoint they are best to put at the scope input. Inserting 1.5K Ohms in series with 100pF to ground gives a decent performing 1MHz cut-off with low DC error.  You can solder the parts between a male and female BNC connector, and then hot glue over it.

Integration of instantaneous power yields energy, and energy divided by time gives average power over the time interval used, such as one cycle of a periodic waveform.

If you are picking up 50Hz, then:

1) Your signals are very small and high impedance. OR
2) You have a ground loop and/or an open ground.

To test for a grounding problem connect the scope probe ground clip to the probe tip.  Without touching the probe tip to anything, place it close to where you would probe in your circuit.  If you pick-up a lot of hum, then there is a strong magnetic field from a transformer or such coupling into the loop formed with the ground clip.  Reduce the exposed area using a high frequency ground clip, and/or add magnetic shielding.

Touch the probe tip to the device under test circuit common with the probe ground clip still in contact witht the probe tip.  If you still pick-up a lot of mains voltage, then check the green wire grounds of the scope and any mains powered gear in the circuit under test.  With the AC power OFF use a DMM to check the resistance between the probe common of the oscilloscope and the circuit common of the circuit being tested.  If there is anything more than an Ohm or two find out why and correct the problem.