Another very important tool for an electronic techlab is a function generator. The one that i am preparing to use is based on the MAXIM MAX038. This chip is rather expensive, yet has many capabilities. It can provide 3 different types of waveforms, triangular, rectangular and sine wave, as well as it provides a TTL output with 50% duty cycle for synchronization reasons. The frequency can be adjusted from 0.1 Hz up to 20 MHz.
The circuit is based on the circuit provided by Maxim. I've done some modifications of course to fit my needs. This is the schematic diagram:
The above circuit covers some of the most important features that a function generator should have. The frequency range can be selected by placing a different capacitor to the COSC input. A 12 positions rotary switch with 12 different capacitors is perfect for this reason. The output frequency can be selected from within the frequency range, by changing the R7 potentiometer. The R6 potentiometer is the fine adjustment for the frequency.
The DADJ input of the chip is the control for the duty cycle of the waveform. I have a switch to either disable it (50% fixed duty cycle), or enable the duty cycle adjustment. If enabled, the duty cycle can be adjusted by the R8 potentiometer.
The output waveform type can be selected from the "FUNCTION" switch. This is a 3-position rotary switch. The common of the switch is driven HIGH, while the two inputs of the chip, A0 and A1 are pulled LOW with 10K resistors. When both inputs are '0', the output is square wave. When A0 is '1', the output is triangular waveform, and when A1 is '1' and A0 is '0', the output is sine wave.
The output is buffered with an OP37Z OP-AMP. The peak to peak amplitude is controlled by the potentiometer R5. By default, the output waveform is symmetrical to the ground. A DC offset can be added to the output if the switch "OFFSET ENABLED" is closed. The DC offset can be controlled by the R22.
@Marc Bonnier i discourage you to use this PCB because it causes a lot of interferences above some MHz. I am not sure if i have any of these PCB files any more (i had a fatal crash some time ago and lost almost all my older project files)
I have a MAX038 chip and I'm planning to make the function generator detailed here. However, I'm having trouble locating the OP37Z op-amp. Do you know where I may be able to find one or can you recommend a replacement?
Hello Jogie. The chip is not produced any more, and is very expensive. I discourage you to copy this circuit. I did this because i had this in stock a lot time ago. If you find it somewhere in stock, it will cost a lot of money. I do not know a replacement part, and i do not think that exists one. But i do know that there are other chips with the same functionality.
Thanks for this site. I now found a fully working function generator, but sir, the chip which u use there is not available in Philippines. Can u recommend another IC to be used that is compatible with your circuit diagram. A replacement for the expensive IC sir coz i cant afford it, our school requires us to make function generator..
Can u send me sir the schematic diagram with their respective components???
The only problem with this project is the chip availability and price. The MAX038 was discontinued by Maxim years ago and one can find it only overpriced on Ebay. Unfortunately there are no direct substitutes and no other chips that go up to 20 MHz as the MAX038 did. The only similar chips around are the XR2206 and the ICL8038 (which has absolutely nothing in common with the MAX038 despite the somewhat similar numeration), both are 20+ years old and both won't go much further one or two MHz.
Nowadays if you want to build a modern signal generator DDS is the solution. Unfortunately it requires an additional MCU, more components and writing code.
I am Anthony Merenda radioamatore with it initials I8CQ, and I am enrolled to grix site Italian web, of electronic amatoriale. And having an integrated maxim 038, I have looked for on the web to find a project and the motor of search google you/he/she has brought me on his/her sito.Visto the project and his/her validity, I ask her if it authorizes me to pubbbicarlo on site web of grix.it. naturally you/he/she will be quoted both his/her site and the planner. aspect his/her news thanks.
antonio snack I8CQ.
P.S. I want to complimenti