A distinctive feature of this circuit is the use of one voltage source of 12 volts and CMOS series microcircuits, namely CD4096, are used as logic elements in the control unit.

This scheme uses 2 welding modes: manual and automatic.

The circuit has the ability to disable pre-gas and post-gas delays if you don’t need them; we’ll call this operating mode without delays. Also, delays can be turned off if we are welding with cored wire (pre-gas and post-gas delays are of no use here).

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The operating algorithm is as follows:

1. When you press the control button, carbon dioxide is supplied first, this is done so that the burner is filled with gas.

2. After a delay of 1..3 seconds, the welding current and wire feed are automatically turned on.

3. After releasing the control button, the wire feed is switched off.

4. Then after 1..3 seconds the supply of carbon dioxide is turned off, this is necessary so that the melted metal does not oxidize when cooling, and the welding current is turned off.

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Manual mode.

The circuit is in its original state, control button SB1 is released. Switch SA1 (Auto/manual) is in the upper position according to the diagram. Switch SA2 (No delays) is in the lower position according to the diagram, that is, the pre-throttle and post-throttle delays are turned on.

When the control button is pressed, logical 1 opens the gas valve through diode VD4. Also starts the delay circuit assembled on D1.1 and D1.2. After the time specified by the chain R6, C4, a logical 1 appears at output 4 of element D1.2, which triggers the motor relay through the diode VD9. At the same time, log 1 appears at output 11 D1.4, which turns on the current relay through the VD6 diode.

At this time, the welding process is underway.

When the control button is pressed, a logical 0 appears at output 4 of element D1.2, which turns off the motor relay. Then, after a time specified by the chain R9, C9, log 0 appears at output 11 of D1.4, which turns off the current relay and gas valve.

At this time the welding is completed.

Auto mode.

The circuit is in its original state, control button SB1 is released. Switch SA1 (Auto/manual) is in the lower position according to the diagram. Switch SA2 (No delays) is in the lower position according to the diagram, that is, the pre-throttle and post-throttle delays are turned on.

The circuit in this mode works according to the same algorithm as in manual mode, only the welding time is set by the chain C2, R5. With these ratings, the welding time is adjustable within 0..15 sec.

I would like to note that the button must be held in this mode. At the end of the time, the circuit itself will stop the welding process.

If you change your mind about welding in automatic mode, just release the control button and welding will stop.

Under No delay mode.

The circuit is in its original state, control button SB1 is released. Switch SA1 (Auto/manual) is in the upper position according to the diagram. Switch SA2 (No delays) is in the upper position according to the diagram, that is, the pre-throttle and post-throttle delays are turned off.

When the control button is pressed, logical 1 through diodes VD4, VD10, VD11 opens the gas valve of the motor relay and the current relay simultaneously, that is, there are no delays. When you release the control button, everything also turns off at the same time.

Same thing in automatic mode.

The mode without delays is needed for the case when we weld with cored wire, when these delays are not needed. Or for some other reason, for example, if there is little gas left (to save money) or you need to quickly grab something, where the quality of the seam is not so important.

Setup.

The device assembled according to this scheme should work immediately without any problems.

The adjustment of the pre-gas and post-gas delay times is regulated by resistors R6 and R9. With these ratings R6, C4 and R9, C9, the maximum delay time is approximately 1 second. If you need more, you can install capacitors C4 and C9 of larger capacity, for example 3 μF.

These capacitors are not polarized. But no one forbids using electrolytic ones instead without changing the circuit.

In automatic mode, you need to select resistor R4 so that there is no empty movement (useless) of resistor R2.