Hello,
i just build a dds with arduino mega and a module with AD9850.
I want to increase the amplitude of the signal. Is that possible with the :
Audio Amplifier Kit - STA540
It is possible but only in the audio frequency range.
What is the frequency range you need out of the DDS?
Have you looked at the AD9850 data sheet and App Notes from Analog Devices? They have example circuits.
If you require a wide frequency range and frequencies beyond audio then Op-amps are the better way to go. You will need an op-amp anyway to convert the current output of the DDS to a Voltage (per data sheet). Then a low pass filter is needed to remove the DDS’s internal switching frequency (CLK in). After that it is typical to gain the filtered output to the desired levels.
The AD9850 is a great chip and I have used it a number of times. So, answer the above questions and I’ll help you with this.
Also discussed here:
The frequencies i use in the project is from 10 up to 1000 hz.
Because i’m new in the electronics, forgive any technical wrong.
I want to amplifie both sine signals that ad9850 emit, with a single potentiometer.
Is that possible?
Ok, 1 to 1000 Hz is well within the audio range so that audio amp should work.
Both signals from the AD9850? What do you mean?
The AD9850 only outputs one signal but with as differential. These are IOUT & IOUTB on pins 21 & 20 and are compliments of each other.
That audio amp kit also has two pot, one for each channel. So the volumes are adjusted separately. The two pots could be replaced with a dual pot (two pots on a common shaft) but would need to be wired onto the PCB.
Since you are just learning and that amp kit is not that expensive it could be well worth it to buy, build and try it with the DDS.
Not to be a killjoy but … is there some reason (given the freq range) to go this route vs a PC with a soundcard (nowadays built in) ?
The chip AD9850 is part of a project. Pc is something else.
Thanks for the help i’ll try it.
Connection question.
I’ll connect IOUT (pin 21) to LEFT in (+) and IOUTB (pin 20) to RIGHT in (+) ?
Incorrect. IOUT and IOUTB are the same signal. They are just compliments (inverted) of each other.Connection question.
I’ll connect IOUT (pin 21) to LEFT in (+) and IOUTB (pin 20) to RIGHT in (+) ?
You only get ONE OUTPUT from the DDS so only need one audio channel or amplifier.
Look at the Evaluation board schematic on page 15 of the AD9850 data sheet. This shows the simple connections for output. R4 on IOUT converts the output current to a Voltage by Ohm’s Law and sets the impedance of the Voltage output. In the eval board (figure 15) R4 is 50 Ohm for a 50Ohm output impedance. IOUTB is then connected to ground through a resistor of half the impedance or 25Ohm.
To use the audio amp you need to use a resistor value that matches the input impedance of the audio amp. Being that the Amp kit’s input goes to a pot (of unknown value) I’ll guess that a 50 to 250 Ohm resistor (R4) should work properly. Then use a resistor of half R4’s value (or two resistors in parallel that are the same value as R4) on IOUTB to ground (R5).
The DDS output to the audio amp would be from J6 in the eval schematic (fig 15).
Excuse me for the questions.
Look at the Schematic of the module i have. (attachment file).
In the green circles is the pins that give me each a sin signal.
I know that i can’t have different frequency for that channels.
I want to amplifie both channels the same Vpp.
After the amplifier i want each sin signal to connect it with bnc connector.
Can you help me how to wire the amplifier.
Thank you in advance
Ok. First that is a PCB layout not a schematic. A schematic looks like Figure 15 in the AD9850 data sheet.
Do you have a link to this board that has a schematic and description?
I was however able to trace out the circuit on the PCB and it looks like OUT is from pin 21 and OUT2 is from pin 20.
It also looks like the required resistor I spoke of are on this board. From what I could trace out that board looks a bit like the Figure 17 schematic in the AD9850 DS. So just hook up the audio amp and give it a try.
Don’t forget to connect the grounds (common) between the DDS board and audio amp.
The requested link:
http://www.elecfreaks.com/store/dds-mod … p-260.html
Now i thing i understand how to connect it.
See at the attchment.
Ok, that link helps a lot.
I’m still not convinced that connecting both outputs to the both channels of the audio amp is the way to go but will not hurt to try it.
Look at the schematic for the AD9850 board in the link.
J4 is the sine (it says square but I think this is wrong) output from pin 20 (IOUTB) using a 100 Ohm resistor for I to E conversion. That is the lower audio channel in your wiring diagram.
The top audio channel in your diagram connects to pin of J7. This is a filter output from pin 21 (IOUT).
Just some explanation to help you understand where your connections are coming from.
Do you have these boards yet?
Do you have an O’scope to see what these signals look like?
Ad9850 i have it already. I test it with osciloscope and the pins in the green circle emit sine.
I’ll order soon the amplifier and i’ll make some experiments.
Good. An O’scope is almost necessary for this project.
What is the Peak to Peak Voltage you see from those two outputs?
Post back to keep us update on your project.
when i emit frequency the Peak to Peak Voltage is 500mV.
Yes i’ll post if i’ll have something knew.
Hello everybody. Happy new year.
Everything work fine with my project.
For audio frequencies this two modules Ad9850 and amplifier kit worked perfect.
The connections I’ve mentioned in previous topics is correct
Ok, that’s great. Thanks for posting back to report your success.
HI all,
I am doing a DDS function generator by using ARDUINO microcontroller and AD 9850 chip module,the output waveform according to data sheet of DDS chip module is 1 V which is too low,therefore I need to design an amplifier for it which can generate output sinewave within 1-20 V.And the problem I am facing right now is when frequency up to MHZ,the output from DDS chip module begin to decrease,when frequency is 38.5 MHz, the output amplitude equal to 250mV.
can you all share of the designing on amplifier circuit ?
THanks
My project continues.
Everything ok with the sine amplification with the corresponding kit.
Now i want to amplify the square wave, is there an equivalent kit?