A series of new Koyo miniature encoders provide a cost-effective solution for size-limited applications. The TRD-MX series light-duty encoders feature a small body with 25mm diameter and 29mm depth. Made with a 4mm diameter solid shaft, the series offers resolutions from 100 to 1,024 pulses per revolution. The encoders are fitted with a two-meter cable with tinned ends and are available with either 5 to 12 or 12 to 24 VDC open-collector or 5 VDC line-driver outputs; the series provides up to 100 kHz response frequency. The TRD-MX series encoders start at $99 and are available for same-day shipping.
Source:
http://www.packagingdigest.com/article/522947-Mini_encoders_for_small_applications.php
