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Hi all,
I started to develop a new SMS Emulator on a small (but great) platform: the STM32F429I Discovery Board. It Is a cheap evaluation board for the STM32 Cortex M4 MCU with a small 2.4 inch TFT. In this stage the project emulate the basic VDP and CPU function (no sound support). The initial beta release source code is avaliable on www.codeforge.com/article/218395
Any suggestion to improve current version will be appreciate !

This is very neat !
As for sound, it should be the easiest aspect ot emulate (right after banker). My PSG emulation core fits into ~100 lines of text.

The major issue for audio is the board itself.
The board hasn't a native audio output (e.g codec). I can use a DAC output for lo-fi sound but a external amplifier must be applied.

You can do PWM, most MCUs have native PWM support too. You only need a capacitor on the IO line to get "analog" output. I am not sure how loud it will be but it is the least costy solution.

Yes the MCU has several PWM output but it is dangerous to drive directly a speaker to prevent damage the MCU in case of speaker failure. In the future I think to adapt one of the small audio shields avaliable on the market.

one NPN transistor is enough to be able to drive a speaker directly. Have an Emmiter Follower config. Signal to B, Power to C, E to your load (though a series capacitor).

I don't agree. This driving method can be valid for direct output of a rectangular wave of a specific frequency in the audio band. In case of implementation a audio signal PWM output usually is required at least a filter (more than a simple capacitor) to shut down the PWM frequency (see class D output stage)
However the project is released as OpenSource and so feel you free to add your audio code or any other improvement.

I meant the transistor to be a buffer on the signal, so it could drive something heavy. Signal being ready analog output. I have had no problems driving 8ohm speakers from a teeny transistor buffer like that (they get quite warm though then).
I am not familiar with the STM though, but its something I will look into sometime in future !

Dart Vader extend my SMS emulator using a VGA adapter to use a standard monitor and a WII controller to play. See the demo video on
Adapter info and source code avaliable on https://sites.google.com/site/suprabotics/

Author	Message
alex_r Joined: 05 Dec 2013 Posts: 5 Location: Italy	STM32F429 SMS Emulator Posted: Thu Dec 05, 2013 8:32 pm
alex_r Joined: 05 Dec 2013 Posts: 5 Location: Italy	Hi all, I started to develop a new SMS Emulator on a small (but great) platform: the STM32F429I Discovery Board. It Is a cheap evaluation board for the STM32 Cortex M4 MCU with a small 2.4 inch TFT. In this stage the project emulate the basic VDP and CPU function (no sound support). The initial beta release source code is avaliable on www.codeforge.com/article/218395 Any suggestion to improve current version will be appreciate !

TmEE Joined: 31 Oct 2007 Posts: 853 Location: Estonia, Rapla city	Posted: Fri Dec 06, 2013 9:20 am
	This is very neat ! As for sound, it should be the easiest aspect ot emulate (right after banker). My PSG emulation core fits into ~100 lines of text.

alex_r Joined: 05 Dec 2013 Posts: 5 Location: Italy	Posted: Fri Dec 06, 2013 4:29 pm
alex_r Joined: 05 Dec 2013 Posts: 5 Location: Italy	The major issue for audio is the board itself. The board hasn't a native audio output (e.g codec). I can use a DAC output for lo-fi sound but a external amplifier must be applied.

TmEE Joined: 31 Oct 2007 Posts: 853 Location: Estonia, Rapla city	Posted: Fri Dec 06, 2013 5:55 pm
	You can do PWM, most MCUs have native PWM support too. You only need a capacitor on the IO line to get "analog" output. I am not sure how loud it will be but it is the least costy solution.

alex_r Joined: 05 Dec 2013 Posts: 5 Location: Italy	Posted: Fri Dec 06, 2013 6:10 pm
alex_r Joined: 05 Dec 2013 Posts: 5 Location: Italy	Yes the MCU has several PWM output but it is dangerous to drive directly a speaker to prevent damage the MCU in case of speaker failure. In the future I think to adapt one of the small audio shields avaliable on the market.

TmEE Joined: 31 Oct 2007 Posts: 853 Location: Estonia, Rapla city	Posted: Fri Dec 06, 2013 6:30 pm
	one NPN transistor is enough to be able to drive a speaker directly. Have an Emmiter Follower config. Signal to B, Power to C, E to your load (though a series capacitor).

alex_r Joined: 05 Dec 2013 Posts: 5 Location: Italy	Posted: Fri Dec 06, 2013 7:24 pm
alex_r Joined: 05 Dec 2013 Posts: 5 Location: Italy	I don't agree. This driving method can be valid for direct output of a rectangular wave of a specific frequency in the audio band. In case of implementation a audio signal PWM output usually is required at least a filter (more than a simple capacitor) to shut down the PWM frequency (see class D output stage) However the project is released as OpenSource and so feel you free to add your audio code or any other improvement.

TmEE Joined: 31 Oct 2007 Posts: 853 Location: Estonia, Rapla city	Posted: Fri Dec 06, 2013 9:02 pm
	I meant the transistor to be a buffer on the signal, so it could drive something heavy. Signal being ready analog output. I have had no problems driving 8ohm speakers from a teeny transistor buffer like that (they get quite warm though then). I am not familiar with the STM though, but its something I will look into sometime in future !

alex_r Joined: 05 Dec 2013 Posts: 5 Location: Italy	Project extension Posted: Sun Jan 12, 2014 2:29 pm
alex_r Joined: 05 Dec 2013 Posts: 5 Location: Italy	Dart Vader extend my SMS emulator using a VGA adapter to use a standard monitor and a WII controller to play. See the demo video on Adapter info and source code avaliable on https://sites.google.com/site/suprabotics/

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