How to Build a Long Duration Timer Circuit Using Transistors

The content describes a very easy long duration timer circuit which utilizes merely a handful of transistors for the meant procedures.
Long duration timer circuits usually include ICs for the processing because performing long duration delays consists of high precision and exactness which happens to be achievable only making use of ICs.
Sometimes our very own IC 555 turns into helpless and inaccurate when long duration delays are expected as a result.
The experienced problems for preserving high accuracy with long durations is essentially the leakage voltage issue and the inconsistent discharging of the capacitors which results in incorrect beginning thresholds for the timer generating mistakes in the timing for each cycles.
The leakages and inconsistent discharge difficulties turn out to be consequently bigger as the capacitor values develop which evolves into crucial for acquiring long intervals.
Consequently producing a lengthy duration timers with ordinary BJTs could possibly be not likely since these devices alone may very well be too basic and simply cannot be estimated for such complicated implementations.
On the other hand the following transistor circuit deals with the above mentioned difficulties credibly which enables you to serve for getting long duration timing with fairly high accuracy (+/-2%)

 


The circuit might be recognized with the aid of the following information:
A temporary push of the push button charges the 1000uF capacitor fully and generates the NPN BC547 transistor, maintaining the position even though the switch is introduced as a result of the slow discharging of the 1000uF via the 2M2 resistor and the emitter of the NPN.
Activating of the BC547 furthermore transforms ON the PNP BC557 which in turns switches ON the relay and the attached load.
The above circumstance carries on provided that the 1000uF is not discharged below the cut off levels of the the two transistors.
The above talked about functions are extremely simple and make a regular timer configuration which might be too incorrect with its efficiency.
In spite of this the addition of the 1K/1N4148 network immediately the transforms the circuit into a greatly precise long duration timer for the following factors.
The 1K and the 1N4148 link makes sure that whenever the transistors work out the latch on account of inadequate charge in the capacitor, the residual charge inside the capacitor is required to release fully by means of the above resistor/diode link via the relay coil.
The above characteristic ensures that the capacitor is totally worn out off and empty for the next cycle therefore has the capacity to generate a clean begin from zero.
Without the above function the capacitor could be not able to release totally and the recurring charge inside would certainly stimulate undefined commence points producing the methods incorrect and unpredictable.
The circuit could possibly be a little more forward improved through the use of a Darlington pair for the NPN enabling the utilization of considerably more value resistors at its base and equally low value capacitors. Lower value capacitors would generate lower leakages and assist to improve the timing precision throughout the long duration counting periods.