点焊机制作
CD4093BC pinout in the same orientation (C) Fairchild Semiconductor
Parts list:
Resistor 1 kohm (R4)
Resistor 9 kohm (R1)
Resistor 40 kohm (R2)
Multiturn or log taper pot 10 kohm (VR1)
3x Capacitor 10 V 10 uF (you can put the extra capacitor in parallel with C2 to make the pulse longer if needed) (C1, C2)
CD4093BC Quad twoinput NAND Schmitt trigger logic gate
The variable resistor VR1 controls the timing. I used a helical potentiometer but a log pot would probably work just as well. The higher resolution is needed for long welding pulse times for which the whisker of VR1 is close to R2. R1 and R2 adjust the range of the voltage divider. Capacitor C2 is also charged through R1. The voltage divider range should be such that at one extreme, continuous welding is just barely enabled (by keeping the button pressed), and the other extreme just barely gives the shortest welding time that may be needed. If the obtainable shortest welding times are unnecessarily long, the capacitor C2 can be made larger. This will make it easier to get also very long pulse times. Doubling the capacitance should double the timing.
A rough approximation on how the voltage across C2 rises after the button is depressed at time t=0 is given by:
VC2=5V?t?(RR2+RVR1)CC2?RR1?(RR2+RVR1)+t?(RR1+RR2+RVR1)
where R is resistance and C is capacitance across a component. RVR1 is the nominal resistance of the variable resistor, not the current set value. The first half of the variable resistor VR1 and the second half of the variable resistor VR1 + resistor R2 act as a voltage divider that feeds a divided VC2 to a Schmitt trigger which will trigger at nominally 3.3 V, ending the pulse.
