The below shown 10 minute simple timer is a form of enhnaced Schmitt trigger, using a combination of an FET and a BJT. This in turn allowed perfect accuracy for the capacitor charge/discharge cycles and produced uniform, consistent timing intervals for each subsequent cycles. This ensured after each timing cycle when the BC557 switched OFF allowed the capacitor's residual charge to completely discharge via the 1K/1N4148 link and the relay coil. I realized the issue and solved it by adding the 1K/1N4148 feedback link across the BC557 collector and the 1000uF capacitor positive pin. This was because of the inconsistent discharging of the 1000uF capacitor which caused inaccurate timing outputs for each subsequent timing cycles. When I initially designed this, it was without the 1K/1N4148 feedback link, which actually made the design rather inaccurate with its timing cycles. Because the same application can be efficiently implemented through a 2 transistor circuit as shown below: The above designs look unnecessarily complex. PCB Layout 1 to 10 minute timer using just two transistors This 1 to 10 minute timer circuit when used along with a 7 segment display circuit as illustrated below could consume around 60mA current so probably a ac/dc adapter would be more preferable than a battery. The proposed circuit can be used for indicating any time interval from 1 to 10 minutes by using all the outputs of the IC 4017.įor getting different ranges of time intervals across each pinout of the IC 4017, the IC 4060 clock can be set with the desired time ranges, for example 2 minutes, 5 minutes, 40 seconds etc. The red LED at pin15 of 4060 IC indicates the counting process by blinking the connected LED until the pin#6 of IC 4017 goes high. Once the final selected interval is elapsed, the circuit latches itself and freezes by supplying a "high" from the relevant IC 4017 output to pin11 of IC 4060. The reset button at pin15/12 of the ICs can be used for resetting the circuit to original state. Where Cx = required value, Cr = random value capacitor (in uF), Rm = time interval noted from Cr (in seconds) Once the interval is known, the value of Cx for achieving 1 minute time may be calculated with the following formula: The IC 4017 is wired in its ususal decade counter mode wherein its outputs shift a logic "high" across its pin3 to pin6 in response to every single minute pulse by the IC 4060 at its pin#14.Īs requested three LEDs are positioned for indicating the elapsing of 5 minutes, 6 minutes and 7 minutes in sequence across the pin1,5,6 respectively, with the relevant selected colored LEDs.įor setting up the IC 4060 with 1 minute intervl at its pin3, we initially use a randomly selected low value capacitor for Cx and then note down the interval at pin3 for this capacitor. In the shown 1 to 10 minute timer with display circuit, IC 4060 is configured as a 1 minute clock generator which is acquired at its pin#3. I would also like to have a seven-segment display show the elapsed time. I would like for it to light a Green LED after 5 mins, then turn off the green LED and light an Amber LED at 6 mins, and then turn off the Amber LED and light a Red LED as well as sound a buzzer at 7 mins. I want it to have an On/Off switch to power the circuit and a Start/Stop button as well as a Reset button. I have a bunch of parts already and I would like to use them if possible. I am trying to build a circuit to help me with giving speeches.
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