I recently purchased this DDS Function Signal Generator

Its specs are below

Display: 1602 LCD
Operating Voltage: DC 7V-9V
DDS Frequency Range: 1Hz-65534Hz
Frequency(HS) Output: up to 8MHz
Section into the Value: 1, 10 , 100, 1000, 10000 Hz
Offset: 0.5pp-5Vpp
Amplitude Amount: 0.5Vpp-14Vpp

I already received it but I do not have an oscilloscope to test the waveforms but all the functions seems to work correctly. But when I meassure the signal output voltage from this function generator with a multimeter at the OUT pin, the value is showing negative voltage in the multimeter.

Is it normal or is there something wrong with the signal generator. When I use a separate 555 timer circuit the output is positive and fine. Why would this output voltage read a negative value.

Any advice will be greatly helpful.

Thanks.

 

the value is showing negative voltage in the multimeter.

How much negative?
What frequency? Many meters do not work well at high frequencies. Try 60hz.

 

If you are getting a minus sign, you are measuring DC volts, you should be measuring AC volts.

 

The left hand pot adjusts the amplitude of the output. The right hand pot adjusts the DC offset of the output. This offset can be adjusted to plus or minus with respect to ground. The version that I have looks the same as the picture in post #1. It only requires a +12 volt input but it has an LCM7660 that generates the negative supply to the op amps. If you turn the right hand pot you should see the DC level of the output change.
With a Fluke114 DMM and a scope connected to the output and the output adjusted to read 1 volt RMS (At 1 Khz sine wave) the scope reads about 2,9 volts peak to peak, This is about right as 1 volt RMS is 2.828 volts peak to peak.

Les.

 

The left hand pot adjusts the amplitude of the output. The right hand pot adjusts the DC offset of the output. This offset can be adjusted to plus or minus with respect to ground. The version that I have looks the same as the picture in post #1. It only requires a +12 volt input but it has an LCM7660 that generates the negative supply to the op amps. If you turn the right hand pot you should see the DC level of the output change.

Thanks. Adjusting the offset seems to work. I am getting positive voltage.

Thanks everyone else for your suggestions.

 

The version that I have looks the same as the picture in post #1.

LesJones,

Nice to know that you have the same version. If you have an operating manual or maker manual for this pls give me a link. I couldn't get it from the seller and according to the seller, its input supply voltage is 7 Volts to 9 Volts DC. But I suppose but not sure that it is 12 Volts. For now I am using a 9 Volt DC power supply.

 

There are many different versions of this basic design. I bought mine several years ago. I think it came from Banggood.
I found a manual for a slightly different version that requires a + & - 12 volt supply. I have attached the file to this post. The version in this manual uses an LM358N (8 pin DIP) op amp. the version of the board that I have uses an N5532 surface mount op amp.

Les.