Check the listing for details. 30-60s counter timer simple stopwatch digital electronic technology DIY Kit. Color: Green, Condition: New. Listed at 10.44 USD. Vocational college electronic skills training kit, digital electronic technology test kit, can also be used for electronic enthusiasts assembly.The power supply voltage of the kit is 5V DC. The kit includes a complete set of components, circuit boards, circuit instructions, etc. The buyer needs to weld and install by himself.Circuit principle:The counter uses the synchronous addition counter CD4518 to count. CD4518 is a decimal addition counter, which contains two identical counters. Each unit has a clock input. Reset is the zero clearing end of the counter. The counting pulse is sent out by NE555. The timer adds one pulse every time it receives a pulse. The switch S1 is used to control the 30s or 60s display. Quantity: 1pcs