LCS-1M - A Full-Featured, Low-Cost Hobby Oscilloscope

This instructable will show you how I developed a simple yet full-featured digital sampling oscilloscope that I hope will enable you to get a successful start in this domain. The main goals in this development were:

Create something that is really usable in practice - i.e. it must have sufficient sample rate to at least cover the audio range (DC up to well over 20 kHz), and a wide input range (from Millivolts up to several Volts). The present design actually is usable up to about 150 kHz (sample rate is 1 MHz = 1 million samples per second). The maximum voltage range is -15 to +20 Volts, but can also go down into the low mV range.

Use only readily available, inexpensive parts which don't need special skills to assemble - e.g. no tiny surface mount components. The whole scope can be put together with a cheap soldering iron, a small wire cutter and flat-nosed pliers.

Keep down cost as much as possible and design it in a way that all the components are easy to procure and assemble, so any moderately skilled hobbyist can build his/her own (see circuit description later).

Make it easy to use so even a user without much experience with oscilloscope gets a quick start, and make it compact so it doesn't use much desk space.

Last but not least, make it an open design so anyone can improve upon it. Note that the design may be used without any restrictions for personal, non-commercial use only. Any other use is strictly prohibited without explicit, written permission by the author.

You can get additional information as well as download the original design files (schematic, layout) and scope software from my oscilloscope homepage. From this site you can also obtain the bare printed circuit board and (as long as I have some left) the fully assembled scope and accessories.

In case you wonder what LCS-1M stands for, it's Low Cost Scope, 1 Megasample/sec.

Good luck!

Disclaimer (yes, this is a litigious world :-):

The author of these pages does not assume any responsibility whatsoever regarding the design, construction or use of the described circuit. The author cannot be held responsible for any damage to persons or property connected with the described design. This includes (but is not limited to) damage to your computer, fitness for a specific task, and specified performance. If you decide to build the oscilloscope and use it, you do so at your own risk. Observe safety guidelines when soldering, as well as when using the oscilloscope. Never apply any voltage exceeding 20V to the oscilloscope inputs.

Step 1 Filling a Niche

An oscilloscope is an invaluable tool for anyone working in electronics. It allows studying electrical signals that are changing over time. Perfect for troubleshooting, monitoring, or simply observing one's electronic creations in more detail.

Unfortunately, even with significant reductions in cost in recent years, a usable oscilloscope remains out of reach for many people who could benefit from it - especially young students just starting out, and many hobbyists on a limited budget. A good low-end standalone scope easily comes in at over US$1000, and even PC-based scopes (which connect to a computer for display and control) usually cost US$300 and above.

On the other hand, most "hobby" solutions (sound-card based or purely microcontroller based) lack sufficient performance and usually are not much more than toys without much practical use. Most of the time they are more like "proof of concepts" that lack any decent frontend (to amplify small signals or attenuate signals) and have bandwidths much too low even for audio.

Of course it is often possible to pick up a decent used analog scope on Ebay for a good price, but most such scopes (cathode ray type) are rather bulky and bothersome, especially for someone without the luxury of a spacious electronics lab, and they often are difficult to use without a good dose of prior experience.

Comments

[rashmi1990]

Hi this design is bit complicated for a beginner

if some body want a easy design then check this link
http://microembeded.blogspot.com/2011/07/two-channel-pcbased-oscilloscope-usb.html

[Eonir]

I have a noob question.

It is mentioned in the instructable that a USB cable can be used to connect the PC with the device. What kind of USB cable is it?
Is it perhaps this one?
http://www.sparkfun.com/commerce/product_info.php?products_id=8312

Can I use a cheaper USB<->RS232 converter instead? To connect it to the audio-jack only a few wires are needed.

[womai]

Pretty any USB-to-RS232 converter cable should work. You can find them for just a couple bucks on Ebay.

Of course you may need to hack the RS-232 connector and attach a 3-terminal phono connector instead, or alternatively replace the scope's phono jack with a DP-9 jack.

[Blackice504]

Hi there i am thinking of building this as i need such a device i can get a $165 real scope but it only has 20mhz bandwidth but it can handle 300volts on the probes. Say i not need to know the voltage and just see the waveform can i use a transformer on this scope to step the voltage down provided that i use a high freq type transformer and also what is the total cost to build this scope assuming i have all the tools? Thank you so much for this instructable i think its great that someone try's to save us money especialy when scopes are such a needed device but so much money.

[womai]

Regarding measuring high voltages, a transformer is not necessary (in addition it would have a lower-frequency cutoff so it won't display any DC offset). All you need is an ohmic divider. Apart from using a 1:10 or 1:20 probe you can also modify the resistive input divider of my scope. Right now its division ratio is 1:4 (100 kOhm and 33 kOhm), so if you make this 1:40 (e.g. use 390 kOhm and 10 kOhm) that achieves the same 1:10 scaling. That said, as also outlined in the disclaimer, I explicitly assume NO RESPONSIBILITY if something happens at such high voltages (e.g. damage to your computer or yourself); anything exceeding 20 - 30V is potentially dangerous or even lethal. You need to know what you are doing and take proper precautions.

[womai]

It comes down to what you need. In some respects the scope you sent the link to is more powerful than my design, and in some it lacks. Most of all, note that it only has one channel (mine has two), so you can't display one signal in relation to another (e.g. clock + data), which is quite a limitation. It does have better bandwidth than my design - 10 MHz vs. 400 kHz (or 1 MHz after upgrade). It has traditional knobs (some people prefer that), but my design makes it easy to e.g. take screenshots, save waveforms in ASCII format to process them in Excel, make numeric measurements with cursors, etc. If you need to extend the voltage range, the most straightforward way is to use a 1:10 or 1:20 scope probe (note that you'll need to make some small changes to the frontend of my scope to be able to use such a probe, because it needs a 1 MOhm scope input; the details are on my webpage and I'll be happy to answer any further questions). With such a probe the input range goes up to +200V and down to -120V (1:10 probe) or +400V / -240V (1:20 probe). So if you need the bandwidth, I'd look for a decent used two-channel cathode ray scope on Ebay - for $170 you should be able to get something useful. If you can live with lower bandwidth and want a more modern design (or like to build things yourself), go for my scope. Building my scope should come to well under $100, less if you can live without the enclosure; most chips it uses you can get a free samples (btw, that includes the Cypress SRAMs). If you did electronics before you probably have quite a few other components (resistors, chip sockets etc.) already lying around, which would reduce expenses even further.

[Blackice504]

Thank you so much for a speedy responce i mostly work with high voltage above 60volts. and you right high voltage is really dangerous even 9volts ac can give you a tingle or two but apart from that after reading that you said its probley best for me to have your scope for testings chips and things and use the bench scope for testing the high voltage it would be a scary thing to see 300volts run down a usb cable then stright into a 3.3 volt south bridge. thank you so much i will build this but later for now i need to play with high voltage as i am building invertor circuits.

[Blackice504]

http://www.jaycar.com.au/productView.asp?ID=QC1920&CATID=12&form=CAT&SUBCATID=628

here is a link to the scope and its a type that is 10mhz as its 20Mhz

[jam BD]

Sooooooooooooooooooooooooooooooo....
professional =D It's really good =D

[stefannasehi]

This has got to be the biggest instructable ever!

[learner1234]

Hello. I am still trying to get the scope to work. The stage I am at now is the computer won't recognize the scope thru the serial port. On two different computers, after loading the programming editor and setting options as 28X2 and COM1, I get a "Hardware not found on COM1" message. I have meticulously traced continuity from the serial end of the cable to the pins on J_SERIAL. I have checked for 5 volts on the power in pin on just about all the ICs. The voltage regulators put out 5.07 volts. There are 1.67 volts between the serial in ( R) pin on J_SERIAL and groung (G) when the serial cable is connected to a computer. The only bad thing that happened was briefly I used a walwart with too high a current rating. The voltage regulator next to JP7 got extremely hot. Now, using a 300mA 9 volt supply , that regulator - screwed to the board- gets pretty darn warm- too hot to touch the screw after several minutes. I don't know what heat tolerance these devices are, but this seems too hot. I'm at a loss about what to do next. Could I have fried the PICAXE microcontroller or another IC when the regulator got too much current? Should I replace the regulator? Is this the stage where I have to sequentially replace ICs? Though I did change the line pwmout FAST_CLK_PWM_CHAN off to add a comma before the word off, and that seemed to correct a syntax error, I'm afraid my diagnostic skills stop there. I'm guessing that IC function could be checked with a logic probe, but have no knowledge of that. I'm not sure what pwmout is, but I checked the syntax in the PICAXE manual. Any help anyone can offer would be appreciated. Attached is the firmware file I modified

[learner1234]

It appears I fixed the syntax error in line 394 by adding a comma before the word "off". The Programming editor seemed to accept the revision and loaded something to the microcontroller. Now, when I insert the power cable, I get three flashes of the LED, then the LED stays on. However, the PC software keeps giving me an error " Could not find an instrument attached to the computer..." I've tried both the new software and the beta software without success. BTW, I switched the JP7 pins to TX. DO you have any suggestions? Thanks

[learner1234]

I have built the scope, using the Ver 1.1 PCB. While trying to download the firmware using Picaxe Programming editor, I consistently get an error code for line 364, pwmout FAST_CLK_PWM_CHAN off, saying "Syntax error". Do you have any insight into this problem? I tried using the Ver 1.3 BAS file, even though I know it is the wrong version, and got the same error.

[davidkr]

Can anybody tell me how exactly to install the voltage regulator? It seems like some voltage regulators need to be bonded to a heat sink via a thermal adhesive. For this project, the voltage regulator appears to be attached directly to the board. Do I still need to use a thermal adhesive? Any advice would be greatly appreciated.

[womai]

Thermal adhesive or thermal paste improves thermal conductivity to the heatsink. That's only necessary when running the regulator at higher power; for a linear regulator the dissipated power is the supply current times the difference between input and output voltage. I run the scope with a 9V supply and the regulators get warm, but not hot, and the regulators aren't even attached to the board at all. I have people telling me that one of the regulators gets hot if supplied with 12V or higher, in this case simply screw it firmly onto the board - the bottom ground plane will act as heat sink. I don't think at these power levels (the scope only uses 170mA of current) you need anything fancier than that.

[learner 123]

Here is another novice question about the power supply. I purchased a " 9 volt, 300 mA" wall wart- nice word- from a local surplus store. The panel mount power jack ( Jameco151777) has three pins. I was expecting 2 pins, V+ and ground. When I measured the voltage at the pins, I was surprised to find 14.4 volts and 7.8 volts Here are my questions. 1. The 14.4 volts is just under the 15 volt maximum, so it is safe to use, correct? Or, should I be worried that the wall adapter is apparently mis- labelled as 9 volts, and discard it and buy another one? 2. What is the purpose of the second, lower voltage, roughly half of the maximum? Do all power plugs have this setup? Is the half voltage pin dependable to use, though in this case it is not enough voltage, being less than 9 volts? Thanks

[womai]

Chances are your 9V (nominal) supply is unregulated. Because it has some internal resistance (the transformer's secondary coil) its voltage will drop when you put a load onto its output. Without any load 14V output is very possible. These simple DC supplies are sized so at maximum load (300mA in your case) they will give approx. 9V, at lower loads the voltage will be higher. The 7805 regulator can take up to >25V so you are safe. The scope takes approx. 170mA so chances are the actual supply voltage will not be much more than 9V anyway. The third ("half voltage") pin is not connected to anything, but is free floating. Chances are you get fooled by capacitive coupling in combination with the high input impedance of your voltmeter. Connect a resistor (maybe 10 kOhm) between this pin and ground and the voltage should disappear.

[learner 123]

Thank You. I sure learned something. The DMM is not always right. Your right, the voltage disappeared.

[learner 123]

Thank you. Should I solder the two resistors ( 180 and 22K ohms) into the IC socket (CONV1) to accomplish upgrade 1?

[womai]

es, bridging the socket pins with the resistors is the most elegant way.

[davidkr]

Thanks. That helps.

[learner 123]

I am assembling the scope, PCB ver 1.1 enclosure and have a couple novice questions. 1. Are the pins on the breakaway headers ( J_LED, J_SERIAL) meant to have hookup wire soldered to them or are there single female leads with crimp connections available for a cleaner assembly? I soldered leads to J_LED and they look functional, but are messy in appearance. Soldering hookup wire to the various panel mount adapters is the most difficult job in the project, to me at least. 2. Is the correct hookup order for the phono connector to J_SERIAL- a ( fattest part of phono plug) to Rx, b ( middle portion of plug) to Tx, and c (tip of plug) to G?? It is not clear to me from the schematic, so I found a PICAXE datafile online that gave this information 3. For upgrade 2, using the 750/249K resistors and 18/43pf capacitors, in parallel, I intend to wrap and solder the capacitor wire on the resistor wire keeping the capacitor and resistor as close as possible, then solder the resistor wire to the PCB. Is this correct procedure? I suppose I will have to do the soldering as quickly as possible to avoid burning the components?

[womai]

1. both solutions will work; soldering wires directly is a bit faster and cheaper (no jumper headers to and jumper cables to buy).

2. please have a look at the ExpressPCB layout file for the pin assignment:

http://www.pdamusician.com/lcscope/design_design_files.html

3. the easiest solution is to solder the resistors onto the board, then stick the capacitor leads under the resistor leads and solder them to the resistor leads. The capacitors and resistors aren't terribly heat sensitive (unlike e.g. diodes or transistors), so the solder speed isn't that critical.

[learner 123]

Thank You for your reply. In this sentence I am asking if I have the correct order on the MALE part of the phono plug- on the serial-phono cable. Is the correct hookup order for the phono connector to J_SERIAL- a ( fattest part of phono plug) to Rx, b ( middle portion of plug) to Tx, and c (tip of plug) to G?

[BlackHawk1200]

I'm collecting all of the parts to make the version with the enclosure, and I'm not quite sure what to do. The enclosure doesn't have any openings in it, and there are no replacement parts that do have holes for the cables. Am I supposed to drill the openings into the enclosure or am I missing something obvious?

[womai]

Sorry for the late answer, out of some reason I never got any notification about your post. Yes, you need to drill the holes yourself, just like I did. It's actually quite simple, because the enclosure plastic is a very soft material, and all you need is round holes (btw, that's one of the reasons I did not use a DB-9 connector for the serial link). Any plain vanilla electric drill is fine for that and will go through like butter. For the bigger holes (BNC connectors) I'd recommend pre-drilling with a smaller drill (approx. 1/3 to 1/2 of final diameter) to assure the big drill stays centered. I'd also highly recommend clamping the plastic parts down when drilling (i.e. DON'T hold them with your hand - this can cause serious injury should the big drill become stuck and start whirling the piece around!).

[baitzzz]

Could CY7C128A-45PC be replaced with MK48Z02?

[womai]

The part you propose seems to be a 0.6 inch wide 24-pin DIP (the data sheet says "wide DIP"), while the CY7C128A-45PC is a 0.3 inch (narrow) 24-pin DIP. So the other part won't fit without some sort of adapter board. You MAY be able to do it by taking a 0.6 inch wire-wrap socket (i.e. one with long leads) and bending the socket leads together so it fits into the circuit board's 0.3 inch wide landing pattern. Otherwise, judging from a quick comparison of the data sheet, they should be pin compatible. The LCS-1M runs pretty slow so memory access time should not be an issue. One other thing, your proposed part is battery buffered - I'm afraid this will would be a quite expensive alternative. You should be able to find other 0.6 inch wide SRAMS that are not battery buffered and thus cheaper.

[kyle.marsh]

I take my hat off to you. If I'd seen this two weeks ago, I may have decided to build this scope for a projects competition my school's electronics club is doing; as it stands I'm building a theremin, but I'll keep this on the radar and will probably end up building it after I graduate. I'll keep you posted if I do.

[jasonangel29]

does any one have a complete parts list for LCS-1M - digital Oscilloscope i just started college for electronic engineering and i am really interested in building this scope to help me with my studies

[womai]

You can get the parts list (also commonly called "bill of materials" or "BOM") from my scope website, go to Design --> Download:

http://www.pdamusician.com/lcscope/design_download.html

Good luck with the scope if you decide to build it. I got quite a few emails from people who successfully put it together without any problems so I dare say the design is solid.

[ebidk]

Do you know if the PC software will work in linux through wine? Or if there is some other linux software that will work with the scope? I'm primarily running linux but I do have one windows box, anyway I was thinking that I might look into porting the PC software to linux if it didn't work already.

[womai]

If the software has free access to the serial port (e.g. COM1) in Wine, my guess would be "yes". You can do a quick check if it starts at all by just downloading the software and launching it under wine. You should get a message that it couldn't find the scope, but it should otherwise start up normally. Second, if you do have a Picaxe microcontroller already you could just put a simple test circuit together (Picaxe + MAX232), burn the scope firmware onto the Picaxe, and see if the program detects it. I had a few requests regarding Linux compatibility, and at least one person I know of is actively working to a platform independent PC software version (Windows, Linux, MacOS), but time will tell if anybody finishes that endeavor.

[ebidk]

I just tried running the software(version 1.05, build 2008-11-19) in wine(1.0) on Kubuntu and it seems to work as you expected it to :) Unfortunately I don't have a Picaxe handy so I can't test the communications part.

[jeremydeath]

Thanks for the great Instructable! After about two months of waiting for all of the parts to come in and about a week of building, I finally finished it! :) It works great, especially for my first oscilloscope. Being a broke teenager, this really helped in working with signals out of my micro-controller. Here is a picture of the finished thing. Note: Sorry about the crappy image quality, I had to take the picture with my phone. :p Once again, thanks for the great design and instructable. -Jeremy

[womai]

Thanks for sharing your success & the picture. I am very glad to see that more an more people successfully put together their scope. Makes my effort worthwhile - after all, my initial goal was to create a simple, affordable scope because I know how much it can help learning electronics (nothing better than being able to actually see what is going on in your circuit); I just wish such a thing had been available when I was a teenager!

[nolte919]

I tried out my scope for the first time today and it worked flawlessly right off the bat. This is the output from the scope, a 5kHz square wave from a Texas Instruments MSP430 microcontroller. My soldering skills are mediocre at best and I'm using a $40 soldering station off of ebay and I still didn't have any trouble. Thanks so much to womai for all the hard work on this. I absolutely love it.

[nolte919]

You mention on the parts list that you can use two 8-pin DIP sockets for one 16-pin DIP socket. Does that always work? Can I use three 8-pin sockets for the 24-pin socket and two 14-pin sockets for the 28-pin socket?

[womai]

Yes, that will work. Although using 8-pin sockets for everything will probably make things more expensive. My idea was that many of those sockets have minimum orders of 10 pieces (they are quite cheap to begin with), so instead of buying ten 8-pin ones (the scope needs 7) and ten 16-pin ones (the scope only needs 1) you could just the the 8-pin ones and use 2 of the remaining 3 to patch together the 16-pin socket. Saves about a buck.

[nolte919]

My circuit board arrived! Thanks. I'm ordering parts and I can't seem to find that "simple RS-232 serial cable (also available from the Picaxe vendor) ending in a stereo phono plug" on the Picaxe webpage. Is that cable only available in kits? How is it wired up if I want to make my own? Also, when I went to try and get samples from Microchip it says samples are temporarily unavailable. I have a real email address with my company. Any idea what my problem is or when samples will become available? I only signed up today on Microchip's website if that makes a difference.