Cheap AD9851 -Based Signal Generator? - Page 1
Forum section: electronics / beginners

author: bullet308
author_rank: Frequent Contributor
timestamp: January 09, 2012, 12:11:13 am
content: Hi:Would anybody care to offer an opinion on this little minimalist signal generator on eBay?http://www.ebay.com/itm/200673882707?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649Right now, I have a pair of elderly Systron Donner pulse generators that seem best suited to classroom demonstrations of what a crappy, ringing square-ish square wave looks like. :-/Extremely high bandwidths are not required. Just something producing clean square, sine, and sawtooth waves that I can afford.Thanks in advance:>>>BULLET>>>PS Specs from the auction below:Description:AD9851 uses advanced DDS technology, direct frequency synthesis, can produce spectrally pure, frequency and phase can be, programming control and stability of a good sine wave. Increased relative to the AD9850 internal multiplier 6, the reference clock just 30MHZ, 180MHZ, they would get the system clock. Design output 0 ~ 70MHZ, effectively reducing the external frequency source phase noise generated.AD9851 Functional Description:* Using AD9851 DDS chip, the external clock is active 30MHZ crystal.* Using seventh-order elliptic filter, cutoff frequency 70MHZ, step 0.04HZ; phase 16, step 11.25.* Sinusoidal output signal, square wave signal, amplitude stability.* 50% duty cycle square Bomo recognized.1, the product design frequency range of 0 ~ 50MHz, step 1Hz, frequency output stable.* Output waveform: sine wave, square wave.* Output signal amplitude stability: 1Vp-p.* Output frequency control: Four keys to operate independently, simple and quick.2, this design can be disassembled into separate modules and AD9851 51 experimental test module* LCD removed, then the short circuit between the AD9851 AT89S52 and remove the child, the circuit board on the left is the independent board of 51 single-chip experiment (with SPI download port), the circuit board on the right is independent of the AD9851 experiment board.* Output interface: signal generator dedicated connector, and a complimentary special signal generator output line.Packing list:1 * DDS signal generator1 * BNC Signal Cable

author: Unknown
author_rank: Unknown
timestamp: January 09, 2012, 03:09:33 am
content: The issue with the Systron Donner generators may be fixable, their pulse generators were fairly well known. Of course the rise time is finite, but it sounds like they either need adjustment or repairs. No idea about the availability of service manuals.There was a recent thread about a similar DDS board, which was not very positive. Two issues obvious from the specs is that it can generate only sines and square waves, no triangular or sawtooth waves, and that the output amplitude is fixed (no mention whether it's constant). 1Vp-p without DC offset is not very well suited for CMOS logic inputs, for example.

author: amspire
author_rank: Super Contributor
timestamp: January 09, 2012, 03:49:31 am
content: For the money, the boards a great value, but they need extra circuitry like an output amplifier and attenuator and dc offset to make them a replacement for a general purpose signal generator. You can get the same thing without the display for about $25 delivered:http://www.aliexpress.com/product-fm/521664134-AD9851-DDS-Signal-Generator-Module-0-70-MHz-2-Sine-Wave-Circuit-Diagram-wholesalers.htmlThese are probably a better starting point if you are going to use it as the heart of a signal generator box. They can talk to a micro with serial protocol or parallel, so that makes them easy to control.Also you can get boards made from the amazing AD9854:http://www.aliexpress.com/product-fm/494293308-Free-shipping-AD9854-DDS-module-with-5-BNC-socket-output-wholesalers.htmlI haven't looked at the AD9851 specs, but some of the AD9854 specs for signal purity are extremely good.Richard.

author: RCMR
author_rank: Frequent Contributor
timestamp: January 09, 2012, 05:15:31 am
content: You might want to watch this video:

author: amspire
author_rank: Super Contributor
timestamp: January 09, 2012, 05:54:24 am
content: If you can live with a 5MHz maximum sinewave, then this is probably a much better alternative from Itead for $59:http://iteadstudio.com/store/index.php?main_page=product_info&cPath=29_31&products_id=450Richard

author: saturation
author_rank: Super Contributor
timestamp: January 09, 2012, 01:03:04 pm
content: Have you looked into the DDS 3x25? Its not a kit, but it does give you quite a bit of capacity for $130 via eBay. See archived eevblog threads.

author: bullet308
author_rank: Frequent Contributor
timestamp: January 10, 2012, 03:36:22 pm
content: Quote from: alm on January 09, 2012, 03:09:33 amThe manual for the Systron Donner 100C seems to be available enough, but then that is the lower-speced and (it seems to me) lower build-quality unit of the pair. The other unit is a 101D, which is nice but I see little evidence that a manual has EVER existed, much less is readily available, even for money. And, they both have switch problems, and the switches seem to be relatively proprietary in nature so I am not sure how fixable those are.I am not surprised that the $50 wonder is not quite all it should be, but am gratified to discover a $130-class instrument (DDS 3x25) that seems to work pretty well and another Arduino-based option to boot.Thanks, all, for the feedback.

author: Unknown
author_rank: Unknown
timestamp: January 10, 2012, 03:47:07 pm
content: Main issue with the DDS 3x25 for every use is mandatory computer control: useful when doing micro controller development and you're at the computer all day, not so great when you're soldering and not looking at your computer, and limited output amplitude. This has been discussed at length in previous threads.

author: bullet308
author_rank: Frequent Contributor
timestamp: January 10, 2012, 04:27:17 pm
content: My computer and electronics bench are integrated, so thats no problem for me.Have a dedicated XP box just to run stuff for the bench, and the Ubuntu box is close at-hand.