minipov voltage

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plausible
 
Posts: 2
Joined: Wed Feb 24, 2010 1:29 am

minipov voltage

Post by plausible »

First off, thanks for the kit! I went back to maker faire the next year and bought another one. This one was never assembled and has lived on a breadboard since I got it. :)

I have multiple questions regarding "voltage".

I initially wired up the system on the breadboard exactly like the schematic. I powered it up at 5V and the test program worked fine. When I tried to program it at 5V, it didn't work. During programming it will usually blink 3 LEDs ( the brightest in the middle ) At 5v that one stayed dark. When I used 3v it worked fine and I could program it ok.( My kit has the 5.1/5.6V zeners I forget which. )

So I programmed it at 3v a simple "counter" program" and it counted all the way through at 3V, but would start over when it counted up so the upper two bits (pin 18 and 19) were lit at when I powered it at 5V. It was like it was getting reset, but pin 1 was not connected to anything.

I have seen in the forum about the zener can cause a reset at >3V, but I don't think this is the same problem. Some programs work perfectly at 5v while others are flakey ( at 3v everything always works ok) The behaviour doesn't change even when I remove all the zeners from the circuit. I'm somewhat baffled at this point. It almost seems that the chip is flakey... Maybe if I tied pin 1 (reset) to vcc that will stabilize it, I think I tried that once but don't remember now.

With the LEDs removed from pins 18 and 19 I can program it at either 3v or 5v just fine. It is like the LEDs are pulling too much current at 5V and interferes with programming.

The circuit I am testing now basically uses only two pins (11 and 12) to clock data into a shift register to light up LEDs, so the cmos inputs cannot be drawing too much current yet it again works perfectly at 3v and about "95% ok" at 5V (some specific pattens will not display correctly - weird )

Anyway, enough of that, was just hoping someone might have insight.

The main reason I'd like to run at 5v is to interface to an LCD module that runs at 5v. :( maybe there is some type of level shifter I can use?

My other "voltage" question is about rs-232. I saw a post (that I cannot find again after going twice through the minipov forum :( ) that you can connect pin3 of the 2313 to pin 2 of the db9 connector and use the usart for one-way (up to the PC) communication. I had already bought a max232 and was going to connect a separate db9 connector for the serial connection. Originally it was going to be 2-way comms, but I really only need to send data up to the pc.

Will 3V minipov really be able to transmit recognizable rs232 signals with no additional hardware or level converters, just a wire?!!

I thought it would need to be at least 8 or 9v. That would simplify my project greatly: datalogging temperature readings every so often to a PC host. Also I thought I saw a post that says the internal clock is not accurate enough for rs232 comms, and had a way to read out and set some internal value to get closer to the desired clock frequency?

Also does anyone have a link to those posts?

Sorry for all the questions in one post, but that's all I have. The forums are great! Some neat projects. I also learned on the forums that USB-serial was slow ( I didn't knwo ir seemed "normal" to me! I get about 5bytes/sec) and I thought that was just as fast as the modem control lines could be bit banged. Now I can't wait to try on REAL serial port and see how much faster it is without the USB overhead! I don't mind waiting though, I'm just happy to have a programmer out of a couple zeners and resistors.

adafruit
 
Posts: 12151
Joined: Thu Apr 06, 2006 4:21 pm

Re: minipov voltage

Post by adafruit »

the 5v power tends to drive the zener diodes so that the reset pin gets pulled low compared to VCC. you should use the kit as it comes, it works pretty well!

plausible
 
Posts: 2
Joined: Wed Feb 24, 2010 1:29 am

Re: minipov voltage

Post by plausible »

Thanks, and yes the kit works great ( I know, I should run it at 3v ;) ). I got the second kit for the chip and zeners in a convenient package so that I could hook up "peripherals" like shift registers, 7 segment displays, speaker, resistive sensors, etc. That has worked well also, at least until I wanted to hook up something that required 5v...

I am thinking of soldering the zeners and 4.7k resistors directly to the db9 connector as the "programmer" and run the five wires to the kit with a header pin connector. The programmer circuit could fit inside thedb9 connector clamshell case and could also be easily separated from the rest of the ckt if it causes any issues.

I'm just having fun playing around with it. I've wanted to get into microcontrollers for years; thanks for making is so easy!

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