Low Freq. (below 1KHz) signal generator ? - Page 1
Forum section: electronics / beginners

author: pilor001
author_rank: Contributor
timestamp: April 24, 2018, 06:48:24 am
content: Greetings...Al in all I am looking for a solution to test my machine Servo controller.Waveform is not too problematic, Voltage + - 5 V should do.Sqr. sinus.. etc. will be fine for this.But the freq. should be LOW.. like 0.3 Hz.... 5 Hz , although the rise / fall times should be fast as possible.Are the 5 - 10 - 20 MHZ generators up to this ? (FY6600 or better to have a Siglent 1CH/2CH?)Or a PCB style is fine too ?Thanks.

author: GerryBags
author_rank: Frequent Contributor
timestamp: April 24, 2018, 08:00:30 am
content: I have an old TTi TG210 2 MHz function generator that claims to go down to 0.2 Hz, but many scopes (particularly the last one I used with it at the low-end) don't do well below about 10 Hz, so I wasn't able to verify that. I doubt the rise times are fast enough for you though. Another option would be a pulse generator with fast rise times and single shot it once every couple of seconds.

author: pilor001
author_rank: Contributor
timestamp: April 24, 2018, 08:39:00 am
content: Was thinking about to make a simple NE55 based panel but then the settings will be pretty limited.. I guess.

author: tggzzz
author_rank: Super Contributor
timestamp: April 24, 2018, 09:01:05 am
content: Search fleabay for "dds function generator", and interpret the spec carefully to see if it matches your requirements - especially voltage and ease of changing specs.No recommendation, but cheap things are available, e.g.https://www.ebay.co.uk/itm/DDS-Function-Signal-Generator-Module-Custom-Arbitrary-Waveform-Sine-Triangle/171925925124If you want programmability, then either expect to pay more or to roll-your-own "front panel" with an arduino etc

author: hirada
author_rank: Regular Contributor
timestamp: April 24, 2018, 12:37:22 pm
content: Slightly more expensive, this one claims to go down to 0.1Hz for Sine, Triangle and Square. No information on the rise/fall time though.https://www.ebay.com/itm/261114462307I do not own such a generator, so I cannot comment, but there are a few videos on youtube for this one. Maybe that helps.

author: Burczyk
author_rank: Contributor
timestamp: April 24, 2018, 12:43:37 pm
content: If you have a signal generator, maybe you could use a frequency divider like a cd4017 and then stretch the pulses?Then the waveform could only be a square wave.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: April 24, 2018, 05:19:21 pm
content: If you don't mind old style the HP 3310A / 3310B spans that range by 1000x either way.

author: pilor001
author_rank: Contributor
timestamp: April 25, 2018, 09:22:45 am
content: Hmm..I was hoping that these DDS (bench type....cheap 5 / 20 /40 MHZ) can actually handle LOW freq. It seems that those are more made for 100HZ and above (maybe 20HZ and more)Typically it seems that AUDIO signal GEN. for low freq. reqs. is a better choice if even it is possible to find a decent one.

author: tautech
author_rank: Super Contributor
timestamp: April 25, 2018, 09:31:32 am
content: Pretty much any of the Siglent AWG's can suit your requirements and their cheapest is the 5 MHz SDG805 @ 199 Euro.https://www.siglenteu.com/waveform-generators/sdg800-series-functionarbitrary-waveform-generators/All but the Pulse (min 500μHz) go down to 1uHz but check the datasheet for output amplitude as in varies with the frequency setting.http://www.siglenteu.com/wp-content/uploads/dlm_uploads/2017/10/SDG800_DataSheet_DS02008-E02D.pdf

author: pilor001
author_rank: Contributor
timestamp: April 25, 2018, 10:51:27 am
content: Have been looking at this SDG 805 too. ... and the SDG 1025Still.... a good question is that.... all the tests (youtube...) are always about the "how high" can we go.... So no real test at the low-low ranges.

author: tautech
author_rank: Super Contributor
timestamp: April 25, 2018, 07:14:39 pm
content: Quote from: pilor001 on April 25, 2018, 10:51:27 amAll I have now is the more modern SDG1032X (30 MHz) but I'll put some screenshots up later and show the 'real' rise and fall times, however I can tell you now they'll meet and better the datasheet spec. A previous SDG1010 demo I had easily met spec and IIRC they were in the single digit ns range.

author: JohnPen
author_rank: Regular Contributor
timestamp: April 26, 2018, 09:18:17 am
content: The cheaper Feeeltech FY3200S will provide an output frequency down to 0.1 Hz in 0.1 Hz increments over your specified range (up to 5 Hz).The rise and fall times are under 40 nsec.

author: tautech
author_rank: Super Contributor
timestamp: April 26, 2018, 11:23:27 am
content: A few screenshots of SDG1032X of squarewave and pulse at max amplitude into 50Scope SDS1202X-EAssorted screenshots.100mHz1Hz10Hz100HzMeasurements don't always give precise indication of rise/fall so there's a zoomed shot that shows the edge better.

author: pigrew
author_rank: Frequent Contributor
timestamp: April 26, 2018, 01:06:46 pm
content: The Siglent SDG2xxx's DDS implementation causes frequency errors at low frequencies. I put a table of errors in the SDG2xxx thread. IIRC, they become quite significant with frequencies less than 10 mHz or so. I don't know if other generators have this issue, but it is something to watch out for.If you want a square wave, you can add a comparator/buffer IC to make edges faster (with a phase noise penalty). Some generators even do this internally.However, for most DDS generators, the rise time is inversely proportional to the max rated bandwidth of the generator.

author: woodchips
author_rank: Frequent Contributor
timestamp: April 26, 2018, 03:49:45 pm
content: Look out for the Feedback function generators.The VPG608 does 0.01 to 1kHzThe FG601 does 0.001 to 1MHzThe SFG606 does 0.01 to 1MHzSome have sweep, variable phase etc.All good reliable analogue instruments.

author: pilor001
author_rank: Contributor
timestamp: April 30, 2018, 12:51:35 pm
content: Did they Debugged this error ?

author: tautech
author_rank: Super Contributor
timestamp: April 30, 2018, 07:44:01 pm
content: Quote from: pilor001 on April 30, 2018, 12:51:35 pmI haven't now got one to check.It's very unprofessional to review equipment without stating the firmware # of the device and although the date on his Tek indicated July 17 there's been 2 firmware updates for SDG1k in the last year.That 1 Hz glitch is not mentioned in these updates:https://www.siglenteu.com/service-and-support/firmware-software/waveform-generators/#sdg1000-series

author: Jwillis
author_rank: Super Contributor
timestamp: May 01, 2018, 02:10:40 am
content: Not sure what evil your up to but if your interested in a VLF signal generator this is a pretty good read.This guy uses frequency dividers and low pass filters to get 0.03 Hz to 185Hz.http://post.queensu.ca/~saavedra/research/papers/2011-IJE-very-LF-oscillator.pdf

author: dwkennedy
author_rank: Newbie
timestamp: May 01, 2018, 02:19:33 am
content: For your purposes, could you use an arduino to generate the ~1KHz pulses? Just modify the "blink" demo program to change the duty cycle and period. Maybe add some potentiometers to the analog inputs so you can tweak the parameters on the fly.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 01, 2018, 02:33:57 am
content: I'm very happy with myFeelTech FY2300. I've used it well below 0.01Hz and up to 20MHz. It's a very capable 2-channel DDS unit and can by programmed via USB or directly.I got mine off eBay. Like many Chinese products, most vendors ship it from China. However, I got mine from a company in Los Angeles that stocked them so I was able to get it within a few days.

author: Brumby
author_rank: Unknown
timestamp: May 01, 2018, 02:38:12 am
content: Quote from: pilor001 on April 24, 2018, 08:39:00 am20 years ago I would have said the 555 timer was the way to go. "Limited" settings could be overcome by having different ranges, with a number of different capacitors on a switch or two and a couple of potentiometers.These days, however, you can wrangle and Arduino Nano clone for the price of a cup of coffee - and you'll be able to program all the variations you could want for servo testing.

author: GerryBags
author_rank: Frequent Contributor
timestamp: May 03, 2018, 04:30:49 am
content: I saw a HP33120A 100 uHz - 15 MHz function generator for sale in the UK for £300 which might do the trick for what you want.http://www.stewart-of-reading.co.uk/index.htm