Summary of Arduino USB
This article describes a low-cost DIY solution for programming Arduino clones using a cheap USB-to-DB9 adapter cable instead of expensive dedicated programmers. The author purchased a $2 eBay cable containing a PL2303 chip but discovered it lacks necessary level converters, failing to work with the 0-5V TTL logic required by Arduinos. Despite theoretical expectations, the project ultimately did not succeed in establishing a functional connection.
Parts used in Arduino USB Interface Project:
- Arduino clone (RBBB, Anarduino, or Boarduino)
- USB to RS232 Serial DB9 Adapter cable
- PL2303 chip (internal component of the cable)
LOG: Made a correction/modification Step 3 and added a picture step 5.
So many Arduino users have RBBBs(Really Bare Bones Board (Arduino)) or Anarduinos or Boarduinos that could use a USB interface to program and power them but don’t want to spend $15-20 for a USB BUB or FTDI cable. This Lazy Old Geek is one of them.
Theory: Most Arduino clones are programmed with a PC using a USB port. Theoretically, they could be programmed with an RS232 port but it is really hard to find a PC with RS232. Some Arduino clones come with a USB converter but most do not. Most require a TTL serial connection. TTL stands for Transistor-transistor-logic which basically means 0-5Vdc logic. So these Arduinos require a USB to TTL converter. One of the more common is the USB-BUB by Modern Devices:
http://shop.moderndevice.com/products/usb-bub
I own one and like it but they’re costly.
So I saw these (see picture) USB to RS232 Serial DB9 Adapter cables on ebay for less than $2 so I bought one. Since I had three weeks to wait for it, I thought about and realized that it probably wouldn’t work as true RS232 has plus and minus 3-15 Vdc signals. The Arduino requires TTL levels which are 0 and 5 Vdc. Nevertheless, I’d already bought it so I took it apart. It apparently had a PL2303 chip in it and I saw no level converters. Anyway, I don’t have any kind of RS232 device to check it with but don’t see how it could ever work with a true RS232. But the other thing is; I couldn’t get it to work with an Arduino. If anyone has gotten one of these to work, please let me know how.
For more detail: Arduino USB
- Why do most Arduino clones require a specific converter?
Most require a TTL serial connection because they need 0-5Vdc logic levels. - What is the cost difference between a USB-BUB and the eBay adapter?
The USB-BUB costs $15-20 while the eBay adapter was bought for less than $2. - Does the PL2303 chip inside the cable convert voltage levels?
No, the author saw no level converters on the PL2303 chip. - Can true RS232 signals program an Arduino directly?
No, true RS232 uses plus and minus 3-15 Vdc signals which are incompatible with Arduino TTL levels. - Did the author successfully program an Arduino with the DB9 adapter?
No, the author could not get it to work with an Arduino. - What type of logic does TTL stand for?
TTL stands for Transistor-transistor-logic. - Is finding a PC with an RS232 port difficult?
Yes, it is really hard to find a PC with an RS232 port.
