Connecting the air muscle for computer control is easy. You can use a Nitinol air valve to electronically control the flow of air to the air muscle. These air valves operate at either 1 to 2 volts DC. The nitonal air valve is rated up to 75 PSI.

For frequent readers of this column that's all you need to know. You can work out the interfacing details yourself. For those of you who are new or are just joining us we will provide a complete interface schematic and description.

To operate an single air valve we only need one pin off the parallel (printer) port, along with a ground, see figure 9. The pin is buffer with a 4050 non-inverting hex buffer. The output of the hex buffer turns on or off a TIP 120 NPN Darlington transistor. The transistor controls the current going to the air valve.

Basic Program

The basic program is short and simple. After finding the printer port address; the following lines control the valve of pin 2. By bringing the DB25 pin 2 high the air valve is opened allowing air pressure to the air muscle. Bringing pin 2 low closes the air valve to the muscle and vents the air from the air muscle.

More Air

The air muscle as it has outline uses compressed air from a PET plastic air storage bottle and foot pump. One can use compressed air from just about any source that's available. For instance you can purchase small compressed air canisters used for air brushing. In fact air brushing supplies may provide you with a list of suitable tubing and fittings to experiment with.

There are a few small air compressors available on the market. The more expensive ones, made for air brush painting have metal storage containers and air pressure regulators. At the other end of the market are the inexpensive 12 VDC portable air compressors used for tire inflation. These compressors typically do not have a air pressure regulator or air storage. However these items may be purchased to make an inexpensive pneumatic system. Do not use plastic PET bottles for air storage with any kind of automatic air compressor. The plastic PET bottles are only suitable for air storage with hand (or foot) operated air pumps.