AWG / Function generator for DHO800 / 900 Series Oscilloscopes - Page 1
Forum section: electronics / testgear

author: Zimmermann
author_rank: Contributor
timestamp: June 07, 2025, 11:26:28 pm
content: Hi,this is my first post here, so hello everybody!I recently designed a daughter board for the DHO800/DHO900 series that adds the "missing" function generator.Have not found a board yet, so I created my own that I want to share with you and release as open source.I know that this is a highly requested feature and production + shipping was only ~53€.(I do not sell this, don't even ask, you need to order this by yourself)I definitly don't want to overload the Rigol hacking thread any more (currently 151 pages!), so we need this new topic...The schematic is attached, full documentation and all necessary files are on github:https://github.com/MatthiasElectronic/AWG_DHO8-900(This is my first project in github, don't know if everything is set up correctly - otherwise please let me know)Hope there will be some nice discussions around here and probably a lot of improvements, but this is working quite nice so farSpecial thanks to:- everybody contributing to the Hacking the Rigol DHO800/900 Scope thread- Pu6k1n for the schematic of the reverse-engineered original AWG, the pinning helped a lot- AndyBig for all information about DHO800 to DHO900 vendor.bin modification- Mechatrommer for inspiration from his own AWG attempt and lots of tiny information- hochohmig.de for providing calculation tools- contributers to KiCad and the library pluginsBest wishes from Bavaria!Matthias

author: dy008
author_rank: Newbie
timestamp: June 09, 2025, 02:47:43 am
content: Wow, amazing work. Great!

author: Zimmermann
author_rank: Contributor
timestamp: June 09, 2025, 09:58:42 am
content: Some updates:Originally, I published this with a picture with no harmonic distortion at all visible in the FFT. This measurement was from the first time I switched this signal generator on. Upon doing further measurements a few days later, I have not been able to reproduce it any more. Instead, whatever I try, THD is somewhere at -60dB (which is also more realistic).Also, I am a bit unhappy with ripple injected from the switching regulators on the mainboard, directly below the AWG board. Sadly, the most sensitive parts are directly above the switching regulators...It is not really bad, because there still is 57dB distance between signal and injected ripple and luckily this is attenuated for smaller signal amplitudes.However, upon achieving perfection, this could be better.The switching regulators on the main board have unshielded magnetics, which obviously is a bad start. Frequencies are ~700kHz and ~1.3MHz.So far I tried grounded aluminum kitchen foil, but this brought only ~3dB. I assume this is due to the mostly magnetic characteristic of this EMI.Additionally adding a floating thin (probably a few 100um) iron sheet proved to be much more affective, causing a total reduction of ~10dB.(In the picture this looks like copper, but this really is iron).Probably I should leave it be as it is right now

author: BrokeEngineering
author_rank: Contributor
timestamp: July 10, 2025, 12:55:30 am
content: Any specific reason to avoid the ground pours on top and bottom layers?

author: KhronX
author_rank: Frequent Contributor
timestamp: July 10, 2025, 06:20:02 am
content: So the output BNC is on this daughterboard, instead of the mainboard? Does it get fastened to the scope housing in any way?

author: Zimmermann
author_rank: Contributor
timestamp: July 10, 2025, 06:18:50 pm
content: BNC connector:Yes, the BNC connector is soldered only on the daughterboard, not the mainboard. It is not fastened to the housing, therefore its is absolutely mandatory to use the mounting holes of the daugherboard to fix the daughterboard to the mainboard. "hochohmig.de" used solderable M3 through hole taps for his board, which is much more professional than my M4 screws+nuts (any easier, as no access to the back side of the mainboard is necessary).In my opinion, this is rigid and stiff enough to have a good quality feeling.In addition:Have a look at the pictures - the BNC connector widens a bit at the bottom, which is a slight press fit if the hole in the case is exactly as wide as the pre-bored hole.This requires that the BNC connector is not pushed all the way into the PCB when soldering it, but you may want to leave a small gap of ca. 1mm anyways to have the top aligned to the trigger out BNC of the mainboard.Ground pours:The inner layers are all ground.On the top, there is no space for any ground pours.On the bottom, there is some space, but there is no reason as both inner layer are ground as well.To be honest, I did not think about pouring ground all over the bottom layer during the design of this board, typically I try to avoid this, as it often creates more problems than it solves.Regarding noise incoupling from the mainboard: Farfield and capacitive nearfield is already shielded by the inner layers. For magnetic nearfield, one more layer of copper won't help much.Also, there are defined impedances on the bottom, so there needs to be sufficient clearance to any ground floods. If you want, you can add some ground pours for your personal design, but you need to connect all the islands to the inner ground planes. Otherwise, EMI performance will be worse.Also, be sure to leave sufficient clearance to all traces to avoid crosstalk. For example, the analog filter can be significantly degraded when done wrong.

author: Chewgallo
author_rank: Newbie
timestamp: July 17, 2025, 06:07:55 pm
content: I decided to make one of these and things seemed fine (power rails looked good, I didn't test the DAC with dummy data though) when I powered the board with a bench supply (I tied AWG_EN to 15V) so I gave it a go on the DHO804. I noticed there was no output. Checking the power rails, I saw that the -6.5V line was good but the 6.5V rail wasn't there. Some quick debugging showed that the AWG_EN was only coming in at 1.05V from the scope main board. I see you put a level shift before the -6.5V LMR54406 (U202) EN pin, but not before the +6.5V LMR54406 (U201) EN pin. So the -6.5.V output enables fine with 15V going to the EN pin but the +6.5V output can't turn on with only ~1V on the EN pin. The LMR54406 datasheet shows a typical EN HIGH threshold voltage of 1.23V (1.1V min, 1.36V max) so that likely explains what's going on.Should be an easy fix to cut the trace going to the +6.5V LMR54406 EN pin and tie it to the level shifted control signal, but before I do that I wanted to double check with you what your thinking was on this and why you did a level shift for one IC but not the other. Curious design decision, maybe I missed something in the datasheet that explains this?

author: Zimmermann
author_rank: Contributor
timestamp: July 17, 2025, 06:20:20 pm
content: There seems to be something wrong on your board, I just measured EN pin on my oscilloscope with the AFG attached: 2.95VTo confirm: When the function generator is switched of, I measure exacly 0V.Maybe a soldering issue or a wrong part is assembled? Is U201 and U202 orientated correctly, this can be mixed up?Please do not try to connect the +6V5 regulator EN pin to the level shift of the -6V5 regulator. This does not work, the pulldown of the -6V5 regulator pulls that pin down to a negative voltage, this could damage the +6V5 regulator. Also, once started, the -6V5 regulator probably never stops operation as the EN pin is clamped to -0.7V over the internal diode in the +6V5 regulator.-> Don't do that, there is something wrong on your board.

author: Chewgallo
author_rank: Newbie
timestamp: July 17, 2025, 06:50:54 pm
content: Interesting, good I checked with you! Yea you're right, I didn't look at the schematic hard enough to see that EN gets pulled to -6.5V, not GND.I did hand assemble a chunk of the board (basically everything that was an 'extended' part for JLC) but the assembly seems fine. I double checked all my joints under a microscope and continuity checked everything for shorts before powering up.Some tests I just did:- With the AWG board disconnected from the scope, AWG_EN to GND resistance is ~11Kohm. This makes sense with 2 22kOhm-ish resistors in parallel. I don't think there's an issue there- I checked the AWG_EN voltage on the scope main board with the AWG board disconnected and get 1.06V at the header pin. So the issue seems to be with the scope main board, not the AWG board.- I checked resistance from AWG_EN to GND on the scope (with the scope unplugged, and AWG board still disconnected) and get 5.6Mohm, so no obvious short there sagging down the voltage.There seems to be something else going on here. I can see the AWG_EN pin go to 0V when the AWG is disabled on the scope so it does seem to be toggling, it just doesn't reach the HIGH voltage that it should. Curious...I assume your 2.95V is coming from an MCU or something else running at 3V3 so maybe I cooked the driving pin. I'll poke around a bit. I might need to add a level shift here though, should be easy enough to hotwire in.

author: yumcca
author_rank: Newbie
timestamp: July 18, 2025, 10:06:38 am
content: can this AWG use for bode plot?

author: Zimmermann
author_rank: Contributor
timestamp: August 02, 2025, 09:51:10 pm
content: Yes, the bode anaylzer does work, tried it today.

author: @
author_rank: Contributor
timestamp: August 14, 2025, 03:51:13 pm
content: I have finished the assembly of V2 and it's working fine. Just shoving a 10X probe tip into the BNC connector, I get a ~11ns rise time on the square wave. I'll have to get proper BNC cables next...Since JLCPCB has a MOQ of 2 for assembly, I'll mail the spare one to anybody in Switzerland for free - no guarantees! Some components are missing, see photo. Just send me a PM. No international mailing, don't ask.Thanks Matthias!

author: illiac4
author_rank: Regular Contributor
timestamp: September 12, 2025, 02:29:24 am
content: How much did it cost to build it using jlc pcb?

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 12, 2025, 04:26:24 pm
content: Quote from: @ on August 14, 2025, 03:51:13 pmcan you show sine wave 100kHz 25mVpp signal out of it? measured with 50ohm terminated coax cable directly to dso setting at 1X. thanks.

author: Zimmermann
author_rank: Contributor
timestamp: September 14, 2025, 04:43:46 pm
content: Quote from: illiac4 on September 12, 2025, 02:29:24 amFrom the github documentation:"I ended up with 34€ on JLCPCB for 5 partly assembled boards and 41€ on LCSC for components for 2 boards, including tax and shipment. This adds up to 75€. It should be ca. 53€ if I only ordered components for 1 board. (05/2025)"Obviously, this depends on the dollar price, the available shipping options and the discounts you get (there are always some coupons on JLCPCB).

author: Zimmermann
author_rank: Contributor
timestamp: September 14, 2025, 05:33:36 pm
content: Quote from: @ on August 14, 2025, 03:51:13 pmI measured the same (@1Vpp), so this seems to be correct.Quote from: Mechatrommer on September 12, 2025, 04:26:24 pmI attached a picture measured on mine - but without a 50 Ohm termination. This is just a 50 Ohm coax cable from the AWG BNC directly connected to the high impedance CH1 BNC.Don't know what you need that for, I hope this helps.Obviously, with 50 Ohm termination you should get exactly half the amplitude.(By the way, at 25mVpp, the 2mV zero offset is very visible)

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 18, 2025, 04:22:58 pm
content: Quote from: Zimmermann on September 14, 2025, 05:33:36 pmthats a quite clean signal. the reason i asked is because my signal is quite nasty, probably due to cheap smps ic or simply poor pcb routing from non-ee person. see attached, its from rev2 pcb, i have rev3 made but havent got time to test it. zero offset is no problem since we can compensate in dso setting. cheers.

author: kd7eir
author_rank: Unknown
timestamp: September 21, 2025, 06:59:19 pm
content: Dang, JCLPCB quoted me $147 plus shipping to get five of these assembled. I'm in the US, so tariffs would probably kill the project.Customs duties & taxes $83.32Grand Total $285.34

author: Zimmermann
author_rank: Contributor
timestamp: September 22, 2025, 04:43:56 am
content: OK, this is not how it should look...Speaking about cheap SMPS, did you change the IC? The one I picked has a forced PWM feature, which is - in combination with the large inductance - mandatory to keep the voltage ripple small and in a high frequency band. This is filtered by the LP filter in front of every component.

author: Zimmermann
author_rank: Contributor
timestamp: September 22, 2025, 04:50:31 am
content: 147$ for production is too much. Does it already include the new Trump tariffs in that price or are they added later?Otherwise, be sure that you chose economic and not standard assembly.

author: kd7eir
author_rank: Unknown
timestamp: September 27, 2025, 07:58:17 pm
content: Quote from: Zimmermann on September 22, 2025, 04:50:31 am$83.32 of that is the Trump tariff.

author: Macguiwer
author_rank: Newbie
timestamp: October 04, 2025, 06:53:08 pm
content: And how do you solve the issue with the key on the front?I see it as very strong to pierce that beautiful cover.