Pennywhistle modem

The Pennywhistle was an early acoustic coupler modem originally designed and built by Lee Felsenstein in 1973, and later commercialized and offered for sale in 1976.

As part of the effort that would lead to the Community Memory bulletin board system, Lee Felsenstein had found an Omnitech modem ("or something like that").

The modem was attached to a Teletype Model 33 ASR machine at Leopold's Records in Berkeley, California and connected to the SDS 940 mainframe computer in San Francisco.

These improvements meant the modem was able to follow changes in the reference tone no matter what the source of that drifting was, local or remote.

[7] Like other acoustic coupled modems, the Pennywhistle design was dominated by the two large rubber cups on the top of the device that were used to hold the handset of a standard Western Electric phone.