can somebody please explain to me the use of R4 and C4 of the transmitter circuit in this diagram ?

http://www.geotech1.com/pages/metdet/projects/twinloop/twinloop.pdf

Thankyou forum team !

 

R4 and C4 control the duration of the pulse for the transmitter. It is a typical monostable configuration for a 555-family device (here labeled Ra and C):

Source: LM555 datasheet

IC1 provides the trigger through C3. R3 is a pull-up.

John

 

thankyou
I realise that in monostable position the total frequency time is defined using the formula "1.1 (R1 * C1)",
also for the ne555 used for IC2 in astable mode the frequency is defined using 1/(Ln(2)*C1*)*(R1+R2),
and the on time (duty cycle) is defined using ln(2)*(R1+R2)*C1, with the off time being ln(2)*R2*C1 (because it is discharging only through R2),

However would you be able to fill me in on info regarding how the CR combination circuit actually does this ? how does it hold on to the signal for x amount of time ? any links to useful websites would be great !

 

The time function simply is based on the rate of charge of a capacitor though a resistor (See: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html ). A comparator allows one to set the point in that voltage v. time curve when the output switches.

John

 

the capacitor will charge upto 2/3 of the supply,then it will be discharged by pin 7, until the next trigger pulse on pin 2, the time taken to charge upto 2/3 is derived from the values of R4C4.

 

I don't believe that is completely accurate, as it ignores the effect of the Control Voltage, pin 5 on the Threshold. Using that voltage to create a VCO and adjust PWM is well documented.



John