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Messages - Keoni29

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TI-Nspire / Re: Cave Story for TI nspire CX
« on: April 28, 2015, 06:14:38 pm »
Without hardware accel blitting is never efficient.

TI-Nspire / Re: Cave Story for TI nspire CX
« on: April 27, 2015, 04:43:48 pm »
Does it run smoother now the new image format is used?

TI-Nspire / Re: Cave Story for TI nspire CX
« on: April 26, 2015, 02:09:58 pm »
I cannot download from that link you gave us. It's stuck at connecting to the site.

Other / Re: Making a sound mixer
« on: April 26, 2015, 03:41:14 am »
Shielding ground and signal ground are not the same thing. They are typically connected to eachother with an inductor, so the current is limited and high-frequency noise is rejected.

TI-Nspire / Re: Cave Story for TI nspire CX
« on: April 26, 2015, 03:37:46 am »
Perhaps you could try converting the files on the calculator at first launch? That way you don't distribute modified files, but rather a converter.

Other / Re: Making a sound mixer
« on: April 22, 2015, 03:06:45 pm »
Thanks, I found another ground loop - either my laptop or my desktop sound card is designed badly: you can create a static noise on line out if they have a common mic on line in.
So you have essentially a T-connector for your microphone? That's not really a good idea, noise won't be the only issue here. You can try capacitive coupling, around 330n should be enough.
That only reduces any DC offset and other low frequency interference. The signal grounds should be isolated from the power supply's ground and most importantly from eachother.

Here is some more reading material:

This differential input also rejects any common mode noise: Static noise introduced in the cable. Because the difference between the two signal wires is amplified any noise common to the wires is not amplified.

Other / Re: Making a sound mixer
« on: April 21, 2015, 07:06:56 am »
This is probably caused by a ground loop somewhere in your system.

You cannot isolate grounds using resistors. The grounds are still electrically connected this way. Instead you could try using audio transformers or optocouplers to electrically isolate the signals. This technique is commonly used to get rid of ground loop interference.

Instead of isolating grounds you could also use differential inputs for the amplifiers. This requires an extra feedback loop on all input amplifiers.
With this method the voltage reference is no longer common ground, but the signal ground. You no longer need to connect all signal grounds together. Edit: They're not completely electrically isolated but you can set a very high input impedance, so they can barely affect eachother.

Other / Re: Audio stuff with a TI-83+
« on: March 12, 2015, 03:20:43 pm »
You're gonna have a hard time locating the audio amplifier inside an old laptop. It is much easier to use a battery powered portable speaker.

Other / Re: Z820 - Z80 computer
« on: March 08, 2015, 12:10:27 pm »
It always makes me jealous when I see one of these. I put some time and money into trying to make a z80 computer, but after a burned rom chip and 2 burned 9/5 v power converters, I gave up the project. 

I destroyed the UART chip today by applying power the wrong way around. Man that really pissed me off. It was such an awesome chip with two uart channels, FIFO buffer and tons of other cool features.
It forced me to go in a different direction with this computer though. I will use an eZ8 microcontroller for handling all I/O operations. The eZ8 has a lot of peripherals built in including two uart channels, timers, flash memory, adc, pwm. The only thing it lacks is the ability to execute machine code from ram. That's what the Z80 is for in this computer. The z80 will be the main CPU and the eZ8 only does the I/O.

Because the microcontroller needs time to respond to the z80 the z80 will be put in a halt state until the microcontroller is done processing the I/O request. This is similar to the way benryves solved this problem on his z80 computer.

This shows that breaking stuff is not always the end of the world.

Other / Re: Z820 - Z80 computer
« on: March 05, 2015, 06:36:27 pm »
I wrote a monitor program for the computer. It's just like the one on the CBS6000. I learned a lot about the z80 in the process.
Source can be found here:

Computer Projects and Ideas / Re: Ping meter
« on: March 04, 2015, 05:20:50 pm »
You made a pretty looking tool :D I love stuff like this!

Other / Re: Z820 - Z80 computer
« on: March 03, 2015, 03:06:23 pm »
I got the serial output to work with the PC16552D UART chip. There were some dodgy solder joints that caused problems with it, but I tracked them down and resolved the problem.

It prints characters at 960 Bytes/second right now, but it can go up to 125kByte/second.

Edit: I wrote a bootloader for it too. Works great.

Other / Z820 - Z80 computer
« on: February 27, 2015, 03:03:56 pm »
Z820 - Z80 Computer

Original post:

First video of a blinking LED program.

The features:
CPU: Z80 @ 20MHz
RAM: 128k
UART: Up to 1.25Mb/s transfer rate
FDC: Not implemented yet.

Sourcecode can be found here: (unoptimized as all hell, cause I am still learning)

Other / Re: CBS6000 - an 8-bit 6510 computer
« on: February 27, 2015, 03:03:37 pm »
Imma wire up a snes controller to the thing and write a simple game for it.

Other / Re: CBS6000 - an 8-bit 6510 computer
« on: February 25, 2015, 09:23:16 am »
I hooked up a VGA video board to the computer. It's kinda slow since it uses the SPI bus, but it works.

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