logic analyzer, need 32ch at 25Mhz each - Page 1
Forum section: electronics / testgear

author: 0db
author_rank: Frequent Contributor
timestamp: May 01, 2020, 01:25:10 pm
content: hiI need to sample 32 digital channels. Signals are asynchronous, the clock of the system is 12.5Mhz, signals should be 1/10 slower and they are all digital 5V TTL.I need to develop custom software on Linux to analyze these signals, and I am thinking about usingfourtwo Saleae Logic Pro 16 in parallel attached to four dedicated USB3 ports.Yes, it's a bit expensive. Something like36001300 Euro just for the LA equipment.I am open to alternatives.

author: Venturi962
author_rank: Regular Contributor
timestamp: May 01, 2020, 01:43:19 pm
content: When you say custom software are you referring to custom signal decoders? If so - you want may to look at DSLogic's latest offering whose software can be expanded via custom decoders:https://www.dreamsourcelab.com/shop/logic-analyzer/dslogic-u3pro32/Datasheet says 50MHz sampling for 32 Channels in Streaming Mode.

author: nctnico
author_rank: Super Contributor
timestamp: May 01, 2020, 01:59:58 pm
content: Quote from: 0db on May 01, 2020, 01:25:10 pmA used Tektronix TLA700 series or an Agilent 16000 series logic analyser. These can be controlled remotely and they cost next to nothing.

author: 0db
author_rank: Frequent Contributor
timestamp: May 01, 2020, 02:42:40 pm
content: Quote from: Venturi962 on May 01, 2020, 01:43:19 pmI need to remote control the LA.The input Impedance looks ... a bit weak 250KΩ // ~13pF. I need something with 1MΩ/10pF at least. Ummm, I may interface a buffer, but I haven't yet understood if I can manage to remote control the U3Pro32 LA.

author: 0db
author_rank: Frequent Contributor
timestamp: May 01, 2020, 02:44:06 pm
content: Quote from: nctnico on May 01, 2020, 01:59:58 pmInteresting idea. Thank you. Where can I manage to get one/two of them?

author: nctnico
author_rank: Super Contributor
timestamp: May 01, 2020, 02:44:33 pm
content: Quote from: 0db on May 01, 2020, 02:44:06 pmEbay. Lots of choice. One is enough because with these logic analysers you typically install acquisition modules / cards to get more channels.

author: 0db
author_rank: Frequent Contributor
timestamp: May 01, 2020, 03:12:47 pm
content: The projectDSViewlooks interesting.Quote

author: Venturi962
author_rank: Regular Contributor
timestamp: May 01, 2020, 05:44:08 pm
content: Assuming that the PC you're using is running Linux w/o a GUI, you might want to read about Sigrok-CLI:https://sigrok.org/wiki/Sigrok-cliThey also have a good list of compatible devices (https://sigrok.org/wiki/Category:Logic_analyzer) - new DSLogic stuff isn't supported yet but is planned. The Salae Logic Pro 16 is supported today by it.

author: maginnovision
author_rank: Super Contributor
timestamp: May 01, 2020, 08:41:38 pm
content: The hantek 4032L is also a decent option for use with sigrok. If you needed you could modify built in driver.

author: TK
author_rank: Super Contributor
timestamp: May 01, 2020, 09:04:27 pm
content: I have the Agilent 1670G that I got on eBay. Very inexpensive... but you need to find the matching PODs. You can get the analyzer for around $200 in the US, the PODs are around $20 (16-channels) each.It has ethernet and TCP/IP, you can control using SCPI and X-Windows for remote access.

author: pigrew
author_rank: Frequent Contributor
timestamp: May 01, 2020, 09:17:25 pm
content: Quote from: 0db on May 01, 2020, 02:42:40 pmYour resistance requirement will be hard to meet (without expensive active probes). Most logic analyzers will have a 100 kΩ // <2pF input impedance. On the used market, getting cheap probes is often harder than finding the logic analyzer itself. It's the capacitance and inductance that normally cause a problem, not the resistance.The Salae Logic Pro 16 appears to have "standard" DuPont connectors. Its datasheet reports "2 MΩ || 10 pF", but that'd be without the capacitance & inductance of the cables. It'll effect signal integrity.I thought that the DSLogic would have lower input capacitance...they come with quite nice probes (coax + impedance matching at the probe tip). My guess is that the 13 pF is their old model and they never updated it. I need to get around to measuring the impedance of mine...I crudely measured the impedance by measuring the waveform of a square wave with and without the LA. To get the measured 95% rise time and DC voltages, I had to model the LA probe as "17p || 260k". So, not so good.(What's a good way to measure the probe input impedance? Measure the rise time of a high impedance output with no probe vs one probe?)As far as DSLogic software, DSView is iffy. There is sigrok support, but it doesn't work with streaming mode.Also keep in mind that these USB units probably won't be able to do any sort of per-channel skew. They'll sample exactly on the clock edge (in synchronous mode).