Delta Pulse - Take 2

[kt315]

this trouble was i did meet. a buyer sent me the board unworking. i found a cause was CD4538's. seems there is 4538 type unworking with general RC circuit.

[Emersonpaz]

Just by exchanging the CD4538BE ci's for the MM74HC4538N, the T4 and T5 times went from 15us to 28us. a compromise for field research of coins and large items

[eduardo1979]

Just by exchanging the CD4538BE ci's for the MM74HC4538N, the T4 and T5 times went from 15us to 28us. a compromise for field research of coins and large items

You have to be careful with that, because the 74HC4538N supports the maximum supply voltage of 6V and Delta Pulse works at 12V or more.

[Emersonpaz]

I hadn't noticed. Thanks for the feedback Eduardo, according to the datasheet 74HC4538 input voltage 2V to 6V while the CD4538 3V to 18V. 74HC4538 is receiving a voltage of 10.23v do you think it won't last long? I remember seeing more users here on the forum using the 74HC4538 on the Delta pulse if I'm not mistaken.

[kt315]

i did look on pcb of Mustang... sniffer... he uses HEF4538B, 15V supply max.

[eduardo1979]

the HEF4538BP is the best option. I also used them when I did the Delta Pulse and everything worked correctly for me.

[Emersonpaz]

I used the CD4538BE I just changed C5 1n5 to 4n7 and had T4 and T5 samples with 41us now it detects a gold ring before with 15us it was not possible to detect a small gold ring.

[kt315]

measure R8. your value is wrong.

[kt315]

decrease R7 to 5-6 K if you so need gold ring. decrease FIRST DELAY WIDTH.

[Emersonpaz]

measure R8. your value is wrong.

No, it's not wrong. 27k next to capacitor 4n7 see the colors. my delta operates at 300hz TX POWER 250uS VT1 heated up.
I did a test today I used a 10k resistor between gate and source VT1 I use (K2545) Toshiba works cold without losing detection range. I used the tips in this attached pdf. Has anyone else tested the 10k resistor between the gate and source of the VT1?

[Emersonpaz]

My layout is different, I copied it from another board 126 x96 mm .

[kt315]

Has anyone else tested the 10k resistor between the gate and source of the VT1?

checked and forget. you will get nothing. if you want the depth just turn the pot POWER clockwise. seems you began try "to squeeze juice from dry lemon" that do every geotecher long before you...
i had see that billion times here... you just waste the time.

[Emersonpaz]

I thought the distance was good considering the size of the coil 26cm.
Test small coil Delta pulse:
https://youtu.be/JGPush6MUME?si=eIHUo_kbW8pkjP6u

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Delta pulse 2
coil 40 cm

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Delta pulse 2