Looking for eBay Sigrok PulseView Compatible Logic Analyzer for RS232 Voltages - Page 1
Forum section: electronics / beginners

author: Electro Fan
author_rank: Super Contributor
timestamp: June 02, 2017, 01:09:12 am
content: Just checking to see if anyone has a particular model/supplier you might recommend for an eBay Logic Analyzer that will handle RS232 voltages (at least +/-15 Volts and preferably +/-25 Volts) and that is proven to work with Sigrok PulseView. 8 channels is sufficient but 16 would be ok too. Thanks

author: Gyro
author_rank: Super Contributor
timestamp: June 02, 2017, 09:02:05 am
content: In terms of cost, your cheapest option would be to buy one of the cheap 8 bit ones (Saleae clones), strap a 3.3V zener across each input to clamp the inputs to logic level and add a series resistor to limit the current due to the higher voltages (something like 10k - 50k).You could probably just get away with the series resistors and rely on the input protection diodes of the input buffers, but the zeners would provide extra protection.IIRC, the input circuit of these clones is just a series resistor (~220R) and a 100k pullup to 3v3 before the 74HC CMOS input.

author: abraxa
author_rank: Frequent Contributor
timestamp: June 02, 2017, 02:28:50 pm
content: If you need to look at RS232 with a LA, you could use a MAX232 (or compatible) to convert the line level to logic level, too. That way, you can use any run-off-the-mill LA that sigrok supports, ideally an FX2-based one.

author: Electro Fan
author_rank: Super Contributor
timestamp: June 02, 2017, 07:30:36 pm
content: Thanks for the suggestions on using diodes/resistors or a MAX232. I'd like to use a FX2-based LA as that is the platform for Sigrok's PulseView. I'm hoping to find a FX2-based LA that is designed to natively run RS232 voltages, but if that doesn't pan out the MAX232 approach looks like a feasible solution. In case I don't find a higher voltage spec'd model, are there any basic FX2 based LA suppliers on eBay that are recommended? Thx

author: Gyro
author_rank: Super Contributor
timestamp: June 02, 2017, 07:53:33 pm
content: I doubt if you'll find a native 8 bit RS232 level FX2 based device.You don't have your country flag set (there are local suppliers in the UK for instance) so I'll have to default to China listings, picked at random. The 8 bit FX2 ones (Salea clones) look like this:http://www.ebay.co.uk/itm/USB-Logic-Analyzer-Device-Set-USB-Cable-24MHz-8CH-24MHz-for-ARM-FPGA-M100-/311769127773?hash=item4896e35b5d:g:QhcAAOSwopRYY5bvThey have different labels but are all the same inside. A Cypress FX2, HC245 buffer, Vreg, crystal, and EEPROM which holds the USB PID/VID, input resistors as I indicated in my last post. They all include 8 channel 24MHz in the description.The alternative is to go for a bare FX2 'eval' board these are also available from many suppliers:http://www.ebay.co.uk/itm/CY7C68013A-56-EZ-USB-FX2LP-USB-Develope-Board-Module-Logic-Analyzer-EEPROM-/291549653382?hash=item43e1b6a986:g:pmAAAOSwIzNXOuhTThese bring out all of the FX2 I/O pins, but I think Sigrok only supports the same specific 8 pins that are used by the Saleae clones. No buffering of course.Google is your friend with these things, it's easy to find teardown information. [Edit: In fact they are all shown and described on the Sigrok site]

author: abraxa
author_rank: Frequent Contributor
timestamp: June 02, 2017, 07:56:53 pm
content: Just like Gyro, I don't think you're going to find a LA that can handle the negative voltages without any external circuitry. Best case the internal clamping diodes will become conductive and produce a short circuit on the data line(s), worst case the internal clamping diodes become overloaded and the LA is damaged.QuoteActually, for boards that break out all 16 GPIOs we support 8ch at 24MHz max and 16ch at 12MHz max.

author: Gyro
author_rank: Super Contributor
timestamp: June 02, 2017, 07:58:12 pm
content: QuoteThat's useful to know, thanks.

author: Electro Fan
author_rank: Super Contributor
timestamp: June 02, 2017, 10:30:41 pm
content: Roger all that. Thanks.FWIW, I took a look through the Sigrok hardware info and it appears that this model might support PulseView and the larger range of RS232 voltages:https://sigrok.org/wiki/IKALOGIC_ScanaPLUSStatus supportedMin/max voltage -35V — 35V

author: abraxa
author_rank: Frequent Contributor
timestamp: June 03, 2017, 11:58:30 am
content: Indeed,https://www.ikalogic.com/scanaplus/actually does mention +/-12V RS232 compatibility. Can you find a good deal somewhere? I'm just curious if it can beat the FX2+MAX232 (or FX+zener/resistor) combo in terms of price.

author: Electro Fan
author_rank: Super Contributor
timestamp: June 03, 2017, 06:18:42 pm
content: Quote from: abraxa on June 03, 2017, 11:58:30 amI think it will be hard to beat the price of a FX2+MAX232 combo.Do you use Sigrok PulseView? / How do you like it?

author: alank2
author_rank: Super Contributor
timestamp: June 03, 2017, 09:16:30 pm
content: There are saleae 16 clones on ebay that say they will do +/- 50v continuous, do they work with sigrok?

author: Gyro
author_rank: Super Contributor
timestamp: June 04, 2017, 11:26:28 am
content: I would take the +/- 50V with a pinch of salt. It's really an intermittent inputprotectionvoltage rather than a usage one.Those Salaea 16 clones (well semi-clones) do include separate ESD protection diode packages (unlike the 8 bit ones), just as well as the inputs go into an FPGA. I think the input series resistor values will be too low for countinuous operation at RS-232 levels without causing excessive loading on your signals and high internal dissipation on the input circuits.You ought to be ok if you include additonal series resistors, try 10k again, in the input leads. RS232 isn't going to be going fast in logic terms, so highish value resistors should be fine.

author: Electro Fan
author_rank: Super Contributor
timestamp: June 04, 2017, 06:21:59 pm
content: Is it feasible for a FX2-based LA to incorporate hardware support for up the higher RS232 voltages? If so, I wonder why we haven't seen such a design?

author: Gyro
author_rank: Super Contributor
timestamp: June 04, 2017, 07:09:50 pm
content: I think because RS-232 is a diminishing (diminished?) market. Everything is USB these days, laptops no longer have serial ports. While async serial protocols are still used, they tend to be at logic level. [Edit for long distances there is RS-422 etc. and of course Internet connected devices are common.]There are other ways to analyse RS-232 data, such as a serial port sniffer and PC software. It's pretty unusual to want to monitor 8 RS232 (or 4 bidirectional?) at the same time on a logic analyser. Low cost logic analysers are targeted at the main use - you can easilly translate RS-232 levels down logic as previously explained.Expensive professional logic analysers do indeed have widely variable logic thresholds but you're not talking professional here.Edit: Not quite sure why you are having such an issue with this, you have two very simple methods on translating RS-232 levels down to compatible logic levels already explained.

author: grumpydoc
author_rank: Super Contributor
timestamp: June 04, 2017, 07:50:23 pm
content: The DSLogic Pro is $99 and claims +/- 30V (DC+peak AC), it is also compatible with sigrok.I have one on order but it hasn't turned up yet, so have no idea whether it is any good.http://www.dreamsourcelab.com/order.html+ a few ebay sellers.This one claims 40V DC + peak AC, I don't know if it is compatible with sigrok, but it does have adjustable thresholds to +/- 6V so could be set to the correct values for RS232.http://www.pctestinstruments.com/index.htmI was put off the price for something merely to tinker with (I found it about £400 in the UK) and it has an extremely modest 2048 sample per channel capacity - it claims this is worth more because it uses compression but even so that feels too small to be useful.

author: ebclr
author_rank: Super Contributor
timestamp: June 04, 2017, 07:55:49 pm
content: This will solve your problem?http://www.ebay.com/itm/MAX232CSE-Transfer-Chip-RS232-To-TTL-Converter-Module-COM-Serial-Board-AD-/112071858489?hash=item1a1800d939:g:GrcAAOSwOtdYTeid

author: abraxa
author_rank: Frequent Contributor
timestamp: June 04, 2017, 11:32:01 pm
content: QuoteWe don't officially support it, though. Support for it was added by users who wanted to see it supported, not us core devs, so if it breaks one day then it'll be up to the "community" to fix it. Just wanted to point that out in case someone wants to buy it particularly for the sigrok compatibility.

author: Electro Fan
author_rank: Super Contributor
timestamp: June 05, 2017, 12:15:12 am
content: Quote from: abraxa on June 04, 2017, 11:32:01 pmThanks/understand.Just curious, given that PulseView is built around the FX2, what is your opinion as to whether the FX2 could be augmented with some additional circuitry to support RS232 levels (+/-25V, or so)? Thx

author: Electro Fan
author_rank: Super Contributor
timestamp: June 05, 2017, 12:22:16 am
content: Quote from: ebclr on June 04, 2017, 07:55:49 pmThanks. That looks like a very cost-effective solution for TX and RX.I'm somewhat interested in finding or maybe building a LA that would work with Sigrok PulseView and that would readily support RS232 voltages on all the pins including RTS, CTS, and DTR.

author: Electro Fan
author_rank: Super Contributor
timestamp: June 05, 2017, 12:28:17 am
content: Quote from: grumpydoc on June 04, 2017, 07:50:23 pmThe LogicPort is a pretty good device - both hardware and software; sometimes they show up used:http://www.ebay.com/itm/Intronix-LOGICPORT-LA1034-34CH-LOGIC-ANALYZER-/252834530723?hash=item3ade1cc5a3%3Ag%3A9FYAAOSwc-tY2tYt&nma=true&si=8w9neVwz%252B04qemY8ElGr%252FSvN59o%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

author: abraxa
author_rank: Frequent Contributor
timestamp: June 05, 2017, 10:53:53 am
content: From my point of view, the issue is just as Gyro described:QuoteI can't tell you how those are designed but I'm willing to bet that those devices simply have internal clamping diodes that start conducting when exceeding a small voltage and series resistors to limit the loading on the data lines you want to measure. They might work but there's no guarantee, especially if the series resistor is too small. Example:http://sigrok.org/wiki/Mcupro_Logic16_clone- the series resistor is only 510 ohms. At +/-12V, that'll draw ~20mA on the data lines, potentially altering the signals.If you want, you could get one, try it out and if it doesn't work, add a MAX232 or zener+resistor "frontend".Personally, I'd just getthis boardand make a little daughter board to stack on top (perfboard is perfect), featuring a bunch of 4V7 zeners and 10k resistors. If you want to have a ready-to-use solution, it'll either be a scanaplus or trial and error.Edit:http://sigrok.org/wiki/File:Xl_logic16_100m_black_pcb_top.jpgshows yet another variant and there you can see 472 resistor arrays, so there are 4k7 series resistors present, which would actually work for you. However, it doesn't (yet?) have sigrok support. Looks like a gamble to me...

author: Electro Fan
author_rank: Super Contributor
timestamp: June 06, 2017, 04:33:28 am
content: Quote from: abraxa on June 05, 2017, 10:53:53 amHi abraxa, Thanks for the info and suggestions. I appreciate it. EF

author: Electro Fan
author_rank: Super Contributor
timestamp: June 06, 2017, 05:04:27 am
content: Silly question,What is the reason this board provides a power connector?http://www.ebay.com/itm/RS232-To-TTL-Converter-Module-COM-Serial-Board-MAX232CPE-Transfer-Chip-atmega16-/181935105403?hash=item2a5c2d657b:g:lIcAAOSwFGNWS9oWWhen many similar boards do not:http://www.ebay.com/itm/MAX232CSE-Transfer-Chip-RS232-To-TTL-Converter-Module-COM-Serial-Board-AD-/112071858489?hash=item1a1800d939:g:GrcAAOSwOtdYTeidhttp://www.ebay.com/itm/1PCS-NEW-MAX232-RS232-To-TTL-Converter-Adapter-5V-3-3V-Module-Board-/401304068325?hash=item5d6f9620e5:g:JusAAOSwVctY5hVY- also supports CTS and RTSIs the extra power connector just to run the larger LEDs? Or something else? Thx

author: Gyro
author_rank: Super Contributor
timestamp: June 06, 2017, 09:04:14 am
content: QuoteNo particular reason, apart from maybe using it to for a self-contained 5V powered RS232-only project that has no other USB connection. No, nothing to do with LED size.All three boards have a VCC pin on their logic headers that you will need to power from the FX2 board.Just one other thing to note, I'm not sure if you have considered this.Each converter board is designed for RS232 bidirectional communications (ie transmit and receive). The MAX232 transceiver chip has two output signals - TX and RTS and two input signal - RX and CTS (assuming I have RTS and CTS the right way round).If you are only interested inmonitoringan RS232 link (both RX and TX signals) then you will need to do some board surgery to route both RX and TX to inputs on the MAX232 (you not be able to monitor RTC and CTS too). This is one reason I prefer the the Resistor+Zener approach, you can only use the receive half of each RS232 transceiver chip if you are only 'snooping' on an interface, not actively transmitting/receiving on it.

author: Electro Fan
author_rank: Super Contributor
timestamp: June 06, 2017, 07:53:06 pm
content: Gyro, Thanks. Is it correct that without adding power that a MAX232 simply passes through the TX and RX signals at their original voltage levels?

author: Gyro
author_rank: Super Contributor
timestamp: June 06, 2017, 08:06:37 pm
content: Hi EF,No, without power the MAX232 won't pass anything through at all.P.S. I really would go with the resistor- Zener approach, it's so much simpler. Just use a series 10k resistor followed by 3V3 or 4V7 Zener (calthode to signal, anode to ground) followed by 1k series resistor to FX2 port pin. The 1k resistor will protect the FX2 internal protection diodes from any overshoot from the Zener). You can knock it up on a piece of stripboard in under an hour, even for 16 channels. It will also pass through normal logic signals (although at slightly reduced switching speed).