This topic is to cover the parts required to build a DDS function generator.
Currently I am working on an inverter board for the DDS 20 function generator to provide the -5V rail for the high speed video op amp that produces the sine wave.
This uses the +5V rail from the DDS 20 to power it and after searching for every kind of inverter and dc-dc chip I came up with the TPS6735.
Schematic
http://i100.photobucket.com/albums/m25/kingrs/inverter_schematic_v1-0.jpg (http://i100.photobucket.com/albums/m25/kingrs/inverter_schematic_v1-0.jpg)
Board
http://i100.photobucket.com/albums/m25/kingrs/inverter_layoutv1-0.jpg (http://i100.photobucket.com/albums/m25/kingrs/inverter_layoutv1-0.jpg)
Blanks
http://i100.photobucket.com/albums/m25/kingrs/inverter_pcb_blank_v1.jpg (http://i100.photobucket.com/albums/m25/kingrs/inverter_pcb_blank_v1.jpg)
Built
http://i100.photobucket.com/albums/m25/kingrs/inverter_built_v1.jpg (http://i100.photobucket.com/albums/m25/kingrs/inverter_built_v1.jpg)
The output voltage is -4.946 volts at 60mA load with about 10mV of ripple although the scope shows about 18mV of noise anyway so its hard to tell what the real ripple is.
The power required by the op amp is about 25mA.
After struggling with removing the existing components I have decided to re-think the layout and drop the PCB directly onto the main PCB and make use of the existing components. The only component I am not sure about is the 7905 voltage reg. and the question is will the regulator cause a drain on the system in passive mode - if so I will need to cut the track.
Regards
Rob
Testing and tools:
AD9835 placed on some SOIC pads.
http://i100.photobucket.com/albums/m25/kingrs/AD9835_on_tracks.jpg (http://i100.photobucket.com/albums/m25/kingrs/AD9835_on_tracks.jpg)
Testing the -5V inverter with a 65mA load.
http://i100.photobucket.com/albums/m25/kingrs/Inverter_testing.jpg (http://i100.photobucket.com/albums/m25/kingrs/Inverter_testing.jpg)
PCB drill press with Dremel
http://i100.photobucket.com/albums/m25/kingrs/Drill_press.jpg (http://i100.photobucket.com/albums/m25/kingrs/Drill_press.jpg)
Konus scope for SMD PCB re-work soldering.
http://i100.photobucket.com/albums/m25/kingrs/Konus20xScope.jpg (http://i100.photobucket.com/albums/m25/kingrs/Konus20xScope.jpg)
Homemade 2 x 8watt UV exposure unit
http://i100.photobucket.com/albums/m25/kingrs/UV_exposure_unit_closed.jpg (http://i100.photobucket.com/albums/m25/kingrs/UV_exposure_unit_closed.jpg)
UV exposure unit with artwork.
http://i100.photobucket.com/albums/m25/kingrs/UV_exposure_unit_open.jpg (http://i100.photobucket.com/albums/m25/kingrs/UV_exposure_unit_open.jpg)
DDS 20 with ali case and collet type knobs (medium on the rotary encoder and small on the sine wave amplitude)
http://i100.photobucket.com/albums/m25/kingrs/DDS20_case_knobs_medium_small.jpg (http://i100.photobucket.com/albums/m25/kingrs/DDS20_case_knobs_medium_small.jpg)
knobs medium and medium
http://i100.photobucket.com/albums/m25/kingrs/DDS20_case_knobs_medium_medium.jpg (http://i100.photobucket.com/albums/m25/kingrs/DDS20_case_knobs_medium_medium.jpg)
knobs large and medium
http://i100.photobucket.com/albums/m25/kingrs/DDS20_case_knobs_large_medium.jpg (http://i100.photobucket.com/albums/m25/kingrs/DDS20_case_knobs_large_medium.jpg)
Delay line compared with the AD9959
http://i100.photobucket.com/albums/m25/kingrs/DS1023-100_AD9959.jpg (http://i100.photobucket.com/albums/m25/kingrs/DS1023-100_AD9959.jpg)
top view under scope
http://i100.photobucket.com/albums/m25/kingrs/AD9959vSOIC_top.jpg (http://i100.photobucket.com/albums/m25/kingrs/AD9959vSOIC_top.jpg)
DS1023-100+ and AD9959
http://i100.photobucket.com/albums/m25/kingrs/AD9959vSOIC.jpg (http://i100.photobucket.com/albums/m25/kingrs/AD9959vSOIC.jpg)
DIL 8 showing just the narrow tips and AD9959, side view of the AD9959 appears to show the leads as quite wide where the underside view shows a much narrower pad.
http://i100.photobucket.com/albums/m25/kingrs/AD9959vDIL8.jpg (http://i100.photobucket.com/albums/m25/kingrs/AD9959vDIL8.jpg)
Regards
Rob
Very nice Rob -- looks like you are well set up there.
9959 -- Wow -- tiny!
I now have the samples for the PIC16F887 microcontroller. 1 x 40Pin DIP and 3 x 44 pin TQFP (thin square flat package).
I have tested the 40 pin DIP in a breadboard and can confirm that using it with the Pickit 2 flash programmer, I am able to do in circuit debugging in assembler.
Next step is to get the code I found that uses the 16F628 and AD9833 to compile in MPASM IDE and convert to run on the 16F887 and use the AD9959:
Description as follows:
Quote;*************************************************************************
; DDS_F_Gen.asm
;
; Processor: PIC 16F628 Clocked at : 25MHz (EXT Osc) DDS CLOCK
;
; (Re)Coded: 26/03/05 Author :MRB
; Revision tracking: Ver. 1.01 :(1st issue, 1 changes/fixes)
;
;*************************************************************************
; FUNCTIONAL OVERVIEW
;
; A DIRECT DIGITAL SYNTHESIS SINE/TRIANGLE/SQUARE FUNCTION GENERATOR
; 0.0Hz TO 10MHz TO 0.1Hz RESOLUTION
; 0.0 TO 10.0 Vpp OUTPUT RANGE TO 0.1V RESOLUTION
; PUSH BUTTON CONTROL, WITH 2 X 16 LCD
;
; THE WAVEFORM IS SYNTHESISED USING AN ANALOG DEVICES AD9833 SPI DDS IC
; THE OUTPUT LEVEL IS CONTROLLED BY AN DS1267 SPI E-POT
;
;*************************************************************************
; Port A I/O allocation
; PIN DIR USE
; RA0 O/P DDS FUNCTION GENERATOR IC SPI BUS FSYNC (PULLED UP)
; RA1 O/P ELECTRONIC POTENTIOMETER IC SPI BUS FSYNC (PULLED DOWN)
; RA2 O/P LCD R/S
; RA3 O/P LCD EN*
; RA4 I/P NOT USED
; Port B I/O allocation
; PIN DIR USE
; RB0 O/P LCD D4 / ALSO SPI BUS CLOCK
; RB1 O/P LCD D5 / ALSO SPI BUS DATA
; RB2 O/P LCD D6
; RB3 O/P LCD D7
; RB4 I/P SWITCH 1,UP (ACTIVE LOW,PULLED UP)
; RB5 I/P SWITCH 2,DOWN (ACTIVE LOW,PULLED UP)
; RB6 I/P SWITCH 3,LEFT (ACTIVE LOW,PULLED UP)
; RB7 I/P SWITCH 4,RIGHT (ACTIVE LOW,PULLED UP)
;*************************************************************************
Hi Rob,
You're doing some great work there! Very impressive! By the way, where did you get that microscope you are using from? I am interested in getting one for my lab as well. How much was it?
God Bless,
Jason O
Hi Everyone,
I posted this on PhysicsForums relating to making a multiple output power supply and thought I would paste it here as well in case any of you may know of any good solutions.
Now I'm looking for a good way to power all the chips on the control board I'm designing. It will be powered by two rechargeable 9V batteries in series for a total input voltage of about ~14V.
The interesting thing is that the chips I am using all require a wide range of voltage inputs. I need to produce 1.8, 3.3, 5, and 12 volts for the different sections of my circuit. I was thinking about just slapping some linear regulators to make all the voltages but quickly realized that these would probably drain my batteries faster than the actual circuit would.
Sooo... I am looking into switching regulators since I know they are much more efficient. In a perfect world, I would like to see if there are any out there that can make all these voltages from one input (or at least some of the voltages anyway). The other thing is I'm trying to find a one-chip solution so that I don't have to add a bunch of external support components. Has anyone here run into anything like this before?
God Bless,
Jason O
Hi Jason,
One of the parts required for the AD9959 function generator is an RF transformer or to be more precise 4 of them:
ADTT1-1+ made by mini-circuits:
http://www.minicircuits.com/cgi-bin/modelsearch?model=ADTT1-1
They cost $3.95 each for a qty of 10 or more.
According to the spec sheet for the AD9959 this is to limit the output current on the 4 output ports.
The AD9959 eval board appears to have a (200MHz) low pass filter on it that you can use if required.
The scope is made by Konus:
http://cpc.farnell.com/jsp/search/productdetail.jsp?sku=PY30980
When I bought it, it was in the sale for about 45 GBP, its now selling for 143GBP!
Various other places are selling different models like the DM5 and DM2.
http://www.ukge.co.uk/UK/prodtype.asp?PT_ID=399
Regarding switching regulators, if you look at the top posting you will see the 200mA -5V inverter, Texas Instruments make a whole range of devices to cover most voltages.
The TPS62110/1/2 is quite a good choice:
http://focus.ti.com/docs/prod/folders/print/tps62110.html
Downside is the package is QFN (0.65mm pin pitch), its brand new and hard to get hold of.
Regards
Rob
Hi Rob,
Thanks for the tips. About the RF transformer, I'm intentionally not using that because it's output only works above 200 kHz, which would cut out most of the usable range for Bob's TPU. In my case, I'm simply replacing the transformer wit ha comparator to convert the sine wave into a CMOS computable square wave that I can use the clock the programmable pulse width chips (see attached circuit diagram).
As for the power supply. I like the idea of using the switching supply for greater efficiency, though I'm going to avoid the QFN packages like the plague :P. Have you seen any switching converters that have all of the support components contained in one package?
God Bless,
Jason O
Hi Rob,
what did you use to take the microscope photos?
I have a stereo microscope, but no way to take photos with it.
Regards, Earl
Hi Earl,
The scope is a Konus Opal #5418 with 2X objective and 10x eyepiece.
I used a Nikon Coolpix 775 (2 megapixels) held at just the right point above one of the eyepieces.
You have to get the angle just right, the height and the position must be in the eyepiece focus centre to get a good circular photo with the cropped edges.
The lighting is provided by a 12W (12V 1 A)halogen lamp built into the scope.
Quite easy to do, no need to pay for an expensive adapter ring.
Although if I did a lot of photos like this, I may actually make up a sort of adapter to fit the camera.
The magnification is only 20x so this could be why the photos are so clear.
Regards
Rob
Hi Jason,
Quote from: Jdo300 on October 10, 2007, 12:41:26 AM
Thanks for the tips. About the RF transformer, I'm intentionally not using that because it's output only works above 200 kHz, which would cut out most of the usable range for Bob's TPU. In my case, I'm simply replacing the transformer wit ha comparator to convert the sine wave into a CMOS computable square wave that I can use the clock the programmable pulse width chips (see attached circuit diagram).
As for the power supply. I like the idea of using the switching supply for greater efficiency, though I'm going to avoid the QFN packages like the plague :P. Have you seen any switching converters that have all of the support components contained in one package?
Not sure about the RF transformer now, I misread the spec thinking it could go down to 0.3 Hz, when it really says 0.3MHz or 300KHz, it will probably be fine all the way down to 10Hz or lower, just need to get Mark to test it on his eval board.
The resistors in the diagram, don't they need to be grounded to AGND rather than set to AVDD?The comparator does look like a preferable method of output - at least the parts are easy to get - although they can be expensive for high speed op-amps like the AD811.
From the AD9959 FAQ I read that the current needs to flow to ground.
With regards to the oscillator, I think I will go with a 125MHz 3.3V low jitter SAW device and use resistors to limit the HI/LO voltage.
I will email the Analog Devices tech support to see what they think.
Regards
Rob
New PCB layout v1.1, not sure if the screw will foul L2 though.
(https://overunityarchives.com/proxy.php?request=http%3A%2F%2Fi100.photobucket.com%2Falbums%2Fm25%2Fkingrs%2Finverter_layoutv1-1.jpg&hash=8dd42e8d76f701091a676c0d7375dfd0f00067e9)
I am the proud owner of a brand new AD9959 evaluation board :):):)
I'll post pics tonight.
OOoooooh I wanna see I wanna see ;D
Mark,
I look forward to seeing the pictures of it, although I will be interested to see how you drive the REF_CLK.
20-30MHz xtal is one way.
Jason,
All my bits have arrived, including a low jitter 125MHz 3.3V SAW oscillator, made by Epson Toyocom (I think) as well as an etch tank for making PCBs.
I have all the bits now to make my own AD9959 function generator, just need to put it all together.
With regards to the AD9959 chip and the SAW oscillator, seeing as these parts are fairly exepensive and difficult(impossible) to remove once soldered in I will be mounting these on surf boards that will sit on a main board. The surf board will contain the standard de-coupling caps and any parts that are needed by default.
These surf boards will make conections to the main board via small "whisker" wires to keep down stray capacitance and held in place by two small nylon bolts.
Regards
Rob
Hey Rob,
Sounds great! I'll be very glad to see how the output waveforms look, especially at high frequencies.
By the way, I'm stuck on the last couple of parts for my control circuit. Here's are links to the posts I made below. They concern the voltage detection circuit and the HV biasing circuit:
http://www.physicsforums.com/showthread.php?t=191440
http://www.physicsforums.com/showthread.php?t=191045
God Bless,
Jason O
Hi Jason,
I read it, interesting stuff on the RMS to DC chip, not a cheap device either.
So these devices output an average voltage over a given time span.
So I guess your uC needs to be able to match the time spans to measure the voltage. If you fix the load with a carbon resistor you should ba able accurately calculate the power.
You need to be careful not to get bogged down with a circuit that does everything - I think measuring output can be added later.
The main thing is working out the codes you need to send to the AD9959 to get it to operate.
I still need to do some more work on the assembler program to complete method for talking to the AD9959.
One option I may try is sending some preset codes to it using the output from the simulator on the Analog website.
Regards
Rob
Hi Rob,
You're right about that. Thankfully, I did figure out how to do both the HV throttling circuit and the voltage measurement circuit. The only reason that I'm even bothering with this is to give the controller the capability to run autonomously to self-regulate the coil; particularly in the event that we can't directly control it while the coil is running. Plus, the measurement capability will help us to do other experiments like frequency and bias sweeps to help tune the coils and automatically find the sweet spots.
But I can say that the design I ended up with the the voltage measurement circuit is greatly simplified now. I'm not concerned about measuring the current and the power but only the voltage. (plus we can calculate the current and power knowing the load on the coil anyway). The simple idea is to just go with a resistor divider with a cap in parallel to help smooth out some of the hash (and short out any RE that might work into the circuit). Then I'll just use an ADC to sample the voltage and send it to the microcontroller.
As for the biasing circuit, I'm keeping that simple too. I decided to go with the Op-amp that I mentioned in the post. After talking to the tech support people at Linear, they confirmed that the op-amp I spaced out would work fine to directly throttle the HV supply IC. Now I'm going to be working on drawing the circuit schematics to tie everything together.
Finally starting to see the light at the end of the tunnel :).
God Bless,
Jason O
Work on the case for the DDS 20 is progressing slowly.
Several pics showing the progress so far, as this is the first attempt I have found problems that will be fixed in the next case. Progress through evolution.
Top view, LCD window not cut out yet.
(https://overunityarchives.com/proxy.php?request=http%3A%2F%2Fi100.photobucket.com%2Falbums%2Fm25%2Fkingrs%2FDDS20cased1.jpg&hash=dac79260b82f6460263cad94a91e478071767cd1)
End view shows where I had to cut into the casing to allow the shield to fit up against the front panel.
(https://overunityarchives.com/proxy.php?request=http%3A%2F%2Fi100.photobucket.com%2Falbums%2Fm25%2Fkingrs%2FDDS20cased2.jpg&hash=5a8ac5088b63d84d8519d479353c07ed55a36bc3)
Regards
Rob
Photo showing DC socket in place.
Also have the LED on/off rocker switch in now, just the BNC sockets to go.
(https://overunityarchives.com/proxy.php?request=http%3A%2F%2Fi100.photobucket.com%2Falbums%2Fm25%2Fkingrs%2FDDS20_case_DC_socket.jpg&hash=f9adae9ddc0b917fe4074f7daae396bcd2ef5dfd)
Hi Rob,
I could not help but to comment on the expert craftsmanship of your controller and case! ;D
I am eager to see it hooked to a coil soon. I know that you will contribute greatly in our quest to see this device work in overunity mode. Great progress and thank you for sharing!
Warm regards,
Bruce
Hi Bruce,
It's not brilliant,some of the holes were out by about 1mm, I cut the window for the LCD larger than needed because I took a chunk out when the router was slowing down and decided to cut I nice curve into the side. Should have held it firm until the router had stopped. (mental note: get workshop assistant).
The rocker switch is very large for the case size and I will mount the next one on the side next to the DC socket.
I scratched the anodized case a few times during drilling - swarf under the workpiece. I got around this after the event by covering it with pvc tape.
The good news is the 3mm foam stuck on the inside pushes the LCD module onto the board and clears up the missing segment problem.
@Ward,
Its taken a few hours to make this one, but it is a prototype and I am getting some special milling drills for cutting the larger holes in the case.
The routing of the LCD window took about 10 minutes, so I am pleased with that. The next one will be a bit neater.
BNC sockets;
1. Square wave
2. Sine wave
3. Programmable pulse width square wave
I have not built the circuit for the last output yet, but this will be to drive the DS1023-100 chip using a PIC to give a pulse from 3ns to about 255ns(I think) in 1ns steps.
Also I will be doing some artwork to print onto tech sheet via laser printer and glue to the case to provide legends for the controls.
I have 4 cases to drill/mill and mark up for you.
I will be leaving the black trim off because it fouls the screws, but more important it is too close the sine wave amplitude control.
Regards
Rob King