Outroot and things

Electronics, programming, computers, and geek stuff by Kevin Darlington

Con­vert­ers

So, my girl­friend bought me a STM32F103 board to play around with that has a RS-232 ser­ial port on it to pro­gram it. Since I haven’t owned any com­puter in the last few years that has a ser­ial port, I needed to get a converter.

I decided to go the cheap route and grab one from dealextreme.com. I fig­ured that since most of these con­vert­ers con­tains the PL-2303 chip that it wouldn’t really mat­ter what I got. So I decided to buy this con­verter for $2.99:

Bad con­verter

I actu­ally bought two of them since I needed one for another devel­op­ment board that I had. So I hooked every­thing up, ran Flash Loader Demon­stra­tor, and sure enough it didn’t work. I tried all sorts of set­tings and speeds. At the low­est speed, I got the thing to upload once out of 20 times.

I took the adapter apart and I can  see in there some miss­ing com­po­nents. Now, this hap­pens all the time in man­u­fac­tur­ing and it’s usu­ally not a mis­take. So it doesn’t really raise a red flag as to that being the prob­lem. I didn’t really test any­thing with a volt meter or an oscil­lo­scope, but my guess would be that it doesn’t do the RS232 volt­ages properly.

Those con­vert­ers ended up being a waste of money for me (luck­ily, not that big of a deal since they were cheap). The prob­lem was that I still needed a con­verter, and what device was I going to trust?

Well, Spark­fun has a good rep­u­ta­tion so I decided to look at their USB to RS232 con­verter. It’s a lit­tle more costly at $13, and it con­tains the same PL-2303 chip. If this con­verter didn’t work, it would be a big­ger hit since I had to pay to ship this thing. The prod­uct descrip­tion men­tioned it was a high qual­ity con­verter. I decided to take their word for it.

Good con­verter

…it worked per­fectly! I could crank it up all the way to 256000 bps and it pro­grammed the STM32 with­out a hitch.

Con­clu­sion

So the moral of the story is don’t go cheap on a USB to RS232 con­verter if you’re going to be pro­gram­ming micro­con­trollers with it. The cheap con­vert­ers may still work with other things, though. But I think the par­tic­u­lar STM32 board that I have is pretty strict on the volt­age lev­els that it receives.

I don’t have any rec­om­men­da­tions on other con­vert­ers to use. All I can say is the one pro­vided by Spark­fun def­i­nitely works and is worth the money.

STM32F103

This entry was posted on Friday, February 12th, 2010 at 3:07 am and is filed under Electronics, Tools. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.