Scope
My first oscilloscope
So, you're at the point where a multimeter alone isn't enough to debug the circuits you're working on. Time for an oscilloscope! First, be aware that a good scope can cost thousands of dollars (pounds/euros/your currency of choice) - depending on your definition of 'good'.
Analog Versus Digital:
Scopes fall into two general categories. Older scopes are generally analog and newer ones (post 1995) are generally digital.
Digital scopes are more intuitive to a modern user. They use an ADC to sample the inputs and then a small computer and monitor (usually LCD but early ones used CRT) to plot the samples. They allow for all sorts of neat tricks like plotting a single period of measurement (the "single" button on a modern scope), as well as on screen measurements and mathematical operations like FFT.
Analog scopes work rather differently; they drive the X- and Y- axis deflection circuits of the CRT (remember, that is cathode ray tube) causing the electron beam to 'sweep' the phosphor on the inside of the tube's face. There are no pixels to address and no defined resolution. The scopes use a sawtooth wave generator to move the beam across the screen's X-axis (the time setting just sets the frequency) and an amplifier to control the vertical position (Y-axis). A threshold detector resets the sawtooth generator and acts as the trigger. A classic US Navy film on the subject
Generally, digital scopes are lighter and more portable, and they are more in demand as they are usually newer. That said, some EE's insist on having both kinds of scopes as you can intuit noise from the fuzziness around the line on analog scopes. Additionally, analog scopes aren't subject to the same kinds of pitfalls from aliasing artifacts that digital scopes can do. See here
Bandwidth:
After checkbox features, like the number of channels, need for single shot capture, etc, the biggest spec that people concern themselves with is bandwidth. The bandwidth of the scope tells you the highest frequency signal it can reliably capture. Scopes can range from a bandwidth of a few hundred kilohertz at the extreme low end, to tens of gigahertz at the high end. Choosing this spec is important in your scope choice. You'll want a scope that will grow with your needs but also should not spend on performance you don't need as you may be throwing away thousands of dollars. If you are only planning on working with audio signals ever, almost any scope will do as the audio band craps out at 20kHz. If you want to investigate an Arduino's clock, you'll probably want around 100MHz -- note here, that an Arduino runs at 16MHz, but these are square waves. A square wave is made up of the fundamental and its harmonics. Therefore, if you connected a 16MHz Arduino clock to a scope with 16MHz bandwidth, you'd see a sine wave, since the square wave's higher components are well above 16MHz.
Unless you're working with high frequency RF -- you probably don't need more than 1-500MHz, if you do, you're probably not reading this FAQ!
Adafruit article on 'scope bandwidth: https://blog.adafruit.com/2012/01/27/why-oscilloscope-bandwidth-matters/
Mixed Signal:
Many oscilloscopes are "mixed signal", meaning that they have inputs for digital channels. Some of these scopes can decode things like I2C and SPI busses and provide tens of digital inputs. It is important to know that these inputs do not give you analog fidelity on those channels, so you can't see misshapen signals. Instead they use circuits to "square up" the waveforms to make them easier to interpret. If you're looking to decode digital signals, it's probably best to use the right tool for the job. Check out logic analyzers and bus sniffers. The Bus Pirate is a classic low end solution with variants available from a number of manufacturers - or you can assemble your own such as the Shukran. A little higher up the chain in terms of features and performance are devices like the saleae logic analyzer.
Manufacturers:
First off, the "big two" high end makers Tektronix and Keysight (formerly Agilent and before that HP) demand a premium. Everyone knows who they are and want them. This isn't entirely baseless, as they are "Cadillacs"; the build quality and fit and finish on their scopes is fantastic. That said, there are hundreds of companies who have made scopes over the years. LeCroy, Rhode & Schwartz, Phillips, B&K Precision, ... the list goes on. If the specs meet your needs for a starter scope, and the price is right, don't pay a premium for a name like Tek or HP.
USB:
USB scopes have become really popular in the last few years. Essentially these are digital scopes that save on cost by omitting the screen and using your PC for processing. They are generally low end, but are really portable, often include low capacity power supplies and signal generators, but many find their interfaces less pleasant than a "physical" instrument.
Prominent examples of USB scopes are the Digilient Analog Discovery 2 for about $280, the Picoscope range and the OpenScope at $150.
Bigger manufacturers like National Instruments have begun to penetrate this market as well.
Recommendations:
The digital scope market is always throwing out new models. It's hard to make firm recommendations, but based on chatter among the Redditors, take a look at these hobby-level 'scopes:
| Make / Model | Bandwidth (MHz) | Channels | Manufacturer price (USD, Aug 2021) | Link |
|---|---|---|---|---|
| Rigol DS1054Z | 50 | 4 | $349 | https://www.rigolna.com/products/digital-oscilloscopes/1000z/#ds1000Z/ds1054z/ |
| Rigol DS1202Z-E | 200 | 2 | $299 | https://www.rigolna.com/products/digital-oscilloscopes/1000z/#ds1000Z/ds1054z/ |
| Siglent SDS1202X-E | 200 | 2 | $379 | https://siglentna.com/digital-oscilloscopes/sds1000x-e-series-super-phosphor-oscilloscopes/ |
| GW Instek GDS-1202B | 200 | 2 | $319 | https://www.gwinstek.com/en-US/products/detail/GDS-1000B |
The current (January 2020) most popular go-to for a low cost bench scope is the Rigol 1054z. It's got 4 channels, and 50MHz and can be software unlocked to offer 100MHz bandwidth (often for free without manufacturer approval, although this may not be legal in your country of residence). The Siglent SDS1202X-E is also a popular choices.
This is just a sample from the manufacturers - many other models are available with different specs and features.
- Manufacturer's prices may not include local sales taxes.
- Check local pricing as there are sometimes special offers.
- Some models make not be available in all regions.
- Prices given in good faith. Do a Web search in your region for suppliers and costs.
Used analog scopes can be found for under $50 if you're a bit lucky and not too choosy, but the downside is they are old, usually uncalibrated and might break tomorrow - which is also problematic because many 'scopes have custom integrated circuits which may be very difficult to source. The Tektronix 465 was a classic analog oscilloscope for teaching and beginners which is still in fairly high demand. The Tek 2225 is also often mentioned.
Community Summary:
When looking at the beginners' oscilloscope market, the /r/askelectronics redditors summarize things thusly:
- Buying new: The Rigol range are worth a look. The Siglent SDS1202X-E is also an often-quoted 'budget' brand / model.
- PC/USB Scope: Only for the most basic of measurements. Go for a proper 'scope if possible.
- Analog or Digital: These days, most new budget stuff is digital, but there are a lot of second-hand analog scopes out there at good prices (compared to new) - but see the next point.
- Second hand analogues? There can be some good bargains out there for pretty decent stuff from the likes of Tektronix and HP/Agilent, but check out the state of the 'scope very carefully because some can be very expensive or impossible to repair due to the age and use of specialised/custom components - you might get a bargain until the 'scope breaks. Look out for: Tektronix 2465A, Tektronix 2225
There's some general guidance here: http://www.usedoscilloscope.org/ The live site is dead. The link takes you to a copy of the site at The Internet Archive.
Search this sub:
title:((oscilloscope OR scope) AND (cheap OR first OR budget OR recommend)))
...You'll find conversations such as these:
revision by Linker3000— view source
