| Electronics > Beginners |
| 555 or Op-amp? |
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| Kilroywashere:
--- Quote from: MarkF on March 18, 2019, 10:48:19 pm ---The ATTiny example is very flexible in the number of waveforms it generates. Essentially, an arbitrary waveform generator. I did it with a PIC16F877A some time ago. However, it is very limited in the frequency that it can generate. I seem to remember that I was only able to generate a maximum frequency of 15KHz with the PIC's max clock freq of 8MHz. --- End quote --- the issue i have with that one is i dont have a 4pin pot .... yours look great tho.... would like to build it just dont have a dds chip...! |
| MarkF:
--- Quote from: Kilroywashere on March 18, 2019, 10:55:20 pm --- --- Quote from: MarkF on March 18, 2019, 09:55:59 pm ---If you would like something more advanced, take a look at a function generator I did with a PIC18F2550 microcontroller, AD9834 DDS chip and a MCP4812 Dual 10-Bit DAC. 1Hz to 10MHz at 5Vpp. Output sine, triangle, square, sine sweep, triangle sweep and PWM waveforms. (Still working on PWM waveform. I may not be able to get the code to fit in the PIC.) . . . Is the 10 or 12 bit DAC on the attiny85 Good enough for your design, could i use that in place of the MCP4812 ?? and can i use a 16x2 lcd screen ? I could use the atmega328p in place of the pic .... --- End quote --- It would but I don't think the ATTiny has a DAC. ?? Also, you will need two DACs. One for amplitude and one for the DC offset. The MCP4812 has two DACs inside. My prototype used a MCP4802 which are 8-bit DACs. I went with the 10-bit version because I wanted a little finer control. They are not very expensive. The killer in the design is the $12USD AD9834 DDS chip. You can use any size screen you want. A 16x2 screen seems small. You would need to scroll through all the inputs required and you would not be able to display all the settings at one time. It's whatever you like and how creative you are at displaying and getting the user inputs. The rotary encoder I use has a push button to change between 'input' mode and 'item selection' mode. The PIC18F2550 has 32KB of memory and the C code is currently using 93% of it. --- End quote --- |
| bd139:
One good starting point for building a function generator is the old Heathkit ET3100 design. It’s basically an opamp wein bridge oscillator and a power amplifier on the output. The thing also has a simple square output. Schematic here: https://www.nostalgickitscentral.com/heath/schematics/heathkit_schema_et3100.pdf After you’ve built it you can add a couple of useful features very easily by adding a pot and opamp: offset and amplitude control. The IC in the design is an LM741 for ref. That’s good to about 20Khz. Most things will work here (don’t use an LM358 though). An LF356 will get you up to about 100KHz or so. The light bulb can be pretty much anything under about 20 volts. You just have to adjust the trimmer for lowest distortion. The difference between this and other designs is it’s actually quite useable as a real bit of test gear. Before I had any money I used this design for about 5 years assembled from scrap. |
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