Kellényi L, Buzsáki G
Physiol Behav. 1977 Sep;19(3):449-50. doi: 10.1016/0031-9384(77)90295-5.
A low cost electronic device is described to record on one a.m. tape track the occurrence of any combination of four signals. The fast read out of recorded signals makes the apparatus reliable and helpful for coding behavioral situation and automatic averaging of event related phenomena. A detailed circuitry is included and discussed.