poor man's IO?

There's a parallel port relay board available at

- 8 relays. They also have a serial version at around $60, iirc.

The parallel port one is actually very simple, and you can find plans for an equivalent all over the 'net, and in a number of books. Basically, an optoisolator, transistor, and a relay.

Well, with USB to RS-232 adapters being $14-$15 plus shipping, it would seem like you could pick your favorite inexpensive RS-232 relay board to go with it...

The parallel port board cited is only $35 assembled.

The same source has a USB I/O board (w/o relays) for just under $50 in kit form. You'll pay far more for anything that's USB, assembled, with relays. That may change now that the $5 Silicon Labs CP2102 chips are available.

The devices at

may work for you. They are available on their own from and are bundled with the Digital I/O Commander at and Home Domination at The USBmicro web site has sample/example programs for using the U401 and U421 devices.

The devices support 16 I/O lines, SPI for I/O expansion or interfacing to SPI devices (D/D, serial pot, etc), stepper motor control, LCD interfacing, and support for Dallas

1-wire devices.

-Rob

snipped-for-privacy@whocares.com (Dave Houston) wrote: I wasn't aware that Silicon Labs now has a version of their USB chip with 4 GPIO ports.

The least expensive RS-232 solution (not USB) I know of uses the 74LV8153 which is in stock at

for $1.58 each. This is a single IC solution for RS-232--> 8-Bit discrete output using one IC and a few passive components.

Writeup and schematic here:

HTH ... Marc Marc_F_Hult

If you have a parallel port, the below two links ares about as simple as you can get doing some I/O. Bottom link is a serial board which you could use via USB to serial adapter.

I got some of these chips a good while back from TI, but wasn't successful in getting them to work. I'll try the schematic wiring and the exe program to see if I can get them going now. Using some cheap 74hct259 latching chips, one should be able to get ~120 individually controllable output lines per 74LV8153 chip.

When I first saw the article (in hard copy), I was struck by the fact that it was needed at because it is possibly the simplest application. It's need comes from the fact that the TI application doc is at best sparse with explanation.. The article I referenced is a bit better and makes clearer the design implications of the IC's low-input-voltage application and shows a handy way to provide two different Vcc's.

Marc Marc_F_Hult

The demo exe program is vey helpful for understanding the byte protocol used by the chip. The fact that it will operate at the lower 4800bps means it might be able to be connected to the very inexpensive RF chips for wireless control. Also should make for easy and inexpensive web controlled applications.

The following are not in the sub$50 range, but interesting nonetheless.