@Vlakpage Yes I certainly should! That would prevent the current drain on the microcontroller from getting too large. This was a quick proof-of-concept bread-boarded device (already disassembled) and there are quite a few other things that could have improved quality, but you're absolutely right - thanks for pointing it out! I'll make a note on the website regarding this.
@nibjb Yeah, it's certainly nice minimalistic project. Now that I think about it, you could just leave out the transistor, and make simple DAC with two (or more) resistors to get the varying amplitude and put it through the cap into the antenna, right? Now that would be nice application for the 6 pin tiny AVRs :)
@mkerna Yes or you fry the I/O drivers. FET is in fact charge controlled device. The gate makes capacitor to the other electrodes and as you know, capacitor conducts AC or simple fast change of voltages (=square wave edge) very well. You know, there are FET drivers with several ampere capability for a reason. In some cases you need as fast switching possible to minimze the linear region losses in the transistor. But anyway, you need to make sure the gate current isn't excessive for your driver.
FM is around 100 mHz, too fast to clock this microcontroller with. However the chip could still generate the audio signal to modulate the FM carrier with!
@nibjb lol, I guess I should have thought through my question a bit more. I was thinking about a beacon idea for my model rocket but my radio in my truck (Yaesu FT-8900R) is FM only and even then, 6 meter is higher than the chip can output.
@1979Iceman you might consider a microcontroller keying a simple canned crystal oscillator. You can get them in various frequencies (50.000 MHz is common). It's described on swharden.com/blog/2010-07-14-high-altitude-balloon-transmitter/ (28MHz) and I even used the same method for 3MHz with my previous project, swharden.com/blog/2011-08-05-i-before-e-except-after-hellschreiber/
This is not Am, this is ASK!!!
Abdulla873 1 month ago
What is the antenna made of? Is it just a wire?
meming4 5 months ago
shouldn't you have resistor between the mcu pin and the fet gate?
Vlakpage 7 months ago
@Vlakpage Yes I certainly should! That would prevent the current drain on the microcontroller from getting too large. This was a quick proof-of-concept bread-boarded device (already disassembled) and there are quite a few other things that could have improved quality, but you're absolutely right - thanks for pointing it out! I'll make a note on the website regarding this.
nibjb 7 months ago
@nibjb Yeah, it's certainly nice minimalistic project. Now that I think about it, you could just leave out the transistor, and make simple DAC with two (or more) resistors to get the varying amplitude and put it through the cap into the antenna, right? Now that would be nice application for the 6 pin tiny AVRs :)
Vlakpage 7 months ago
@Vlakpage No. FET gates draw essentially no current. They only need the presence of a voltage, which is what the "FE" part means: "field effect".
mkerna 4 weeks ago
@mkerna Yes or you fry the I/O drivers. FET is in fact charge controlled device. The gate makes capacitor to the other electrodes and as you know, capacitor conducts AC or simple fast change of voltages (=square wave edge) very well. You know, there are FET drivers with several ampere capability for a reason. In some cases you need as fast switching possible to minimze the linear region losses in the transistor. But anyway, you need to make sure the gate current isn't excessive for your driver.
Vlakpage 4 days ago
Sweet beacon idea!
sterwing 7 months ago
FM is around 100 mHz, too fast to clock this microcontroller with. However the chip could still generate the audio signal to modulate the FM carrier with!
nibjb 7 months ago
@nibjb lol, I guess I should have thought through my question a bit more. I was thinking about a beacon idea for my model rocket but my radio in my truck (Yaesu FT-8900R) is FM only and even then, 6 meter is higher than the chip can output.
1979Iceman 7 months ago
@1979Iceman you might consider a microcontroller keying a simple canned crystal oscillator. You can get them in various frequencies (50.000 MHz is common). It's described on swharden.com/blog/2010-07-14-high-altitude-balloon-transmitter/ (28MHz) and I even used the same method for 3MHz with my previous project, swharden.com/blog/2011-08-05-i-before-e-except-after-hellschreiber/
nibjb 7 months ago
@nibjb Thanks! I like the simplicity of the design and that is perfect for what I need.
1979Iceman 7 months ago
Do you think you could do the same with an FM signal?
1979Iceman 7 months ago