Ok, I'll bite ;-) What are you "playing with"? What you need depends on what you want to measure.
Right now, basic homebrew circuits. I've been playing with a electric meter reader (its in the 'lm311' thread last month).
It was working pretty good on a protoboard then I soldered it up last week. It still works, but now I get multiple counts as if the laser lit up the photoresistor two or three times. Can't see anything with the LED indicator or a DVM. If I had a scope, I could compare the voltage level returned from the photoresistor and the output of the LM311 to determine where the problem is. If the input voltage was jumping across the threshold I could look there, or if the input voltage looks right and the LM311 was triggering multiple times maybe I burned it up. And I'd like to be able to record something like that and play it back for analysis. That's my immediate need and seems like a good excuse to get a scope.
Analyzing X-10 and INSTEON signals requires viewing signal in the range of 120khz/131.5khz. And one typically wants two channels (AC line and isolated X10/INSTEON component) which effectively means >600k samples/second.
The first scope you cite has inadequate bandwidth for X10.
The first scope (hobbylab)
- number of channels 2
- sample rate 100 Hz...200 KHz
- memory depth
buffer reading: 1126 sample/channel (1 channel), 563 sample/channel (2 channels)
pipe reading: 64K sample/channel (1 or 2 channels)
- input voltage -20...+20 V (hardware 2 sub-band)
- input impedance 1 MOm
- ADC capacity 10 bits
The third scope only has one input as best I can determine which would eliminate it from consideration (for me) for almost everything.
The third scope (ebay) says it has 2 channels, and it does have CH1 and CH2 on the box.
Max Sample Rate: 100MS/s
Buffer Size: 32K Samples
Voltage Range: 10mV, 20mV, 50mV, 100mV,200mV, 500mV, 1V, 2V, 5V
Is that 100 million samples/sec? That's a big jump from 200Khz. Or are they measuring the same thing using different scales and if so how do you compare hz to samples/sec?
The second scope has adequate bandwidth and two channels. Like most of the inexpensive digital scopes it has 8-bit ADC (one part in 256) which you may find adequate.
The second scope, the POscope, says it has a 10-bit ADC. It has about the same specs as the first scope.
Number of channels: 2
Sample rate: 100 Hz to 200 kHz
Buffer reading: 1126 samples/channel (1 channel), 563 samples/channel (2 channels)
Pipe reading: 64k samples/channel (1 or 2 channels)
Input voltage: -20 to +20 V (hardware 2 sub-band)
ADC capacity: 10 bits
One potential drawback with this and all other PC-based scopes is that they are entriely dependent on the software. I've had three SW based scopes and find them all frustrating in one way or another.
Please elaborate. Was it with the user interface, performance, ??
The 4th scope, the bitscope, the expensive one, only has 1 channel.
Have you considered and rejected a good used _analog_ scope? There are plenty of good ones to be had on eBay for less than your target of $250.
Not entirely. But I don't need another piece of equipment sitting around that will only get occassional use. Then there's the "good used" factor and how do you know for sure? How many "as is" scopes do I need to buy to find a good one?