An inexpensive mechanism for programming multiple variable-interval schedules of reinforcement.

Dukhayyil et al. (1973) drew a wiring diagram for a cheap VI schedule box.

They used simple relays, a timer, and a pulse counter. No computers. No pricey lab gear.

The note tells you how to build it, not what it proves.

No data, no graphs. The paper is a recipe, not a result.

It shows the parts list and wiring so any lab can copy it.

Renne et al. (1976) later used a VI box like this with college students. Button pressing rose when money came faster. The cheap relay design made the study possible.

Locurto et al. (1976) ran concurrent VI schedules with pigeons. Birds under-matched grain rates. Their rig likely copied the 1973 relay plan.

Smith et al. (1975) tried the same setup and saw messy matching. Again, the low-cost programmer gave them tight control.

Across these follow-ups, the same simple box keeps showing up. It quietly powers decades of matching-law work.

If you run VI sessions in your lab, you can skip the $5,000 software suite. Build this $50 relay box instead. It still times reinforcers as well as modern code. Use it for concurrent schedules, change-over delays, or shock timing. Your budget stays intact and your data stay clean.