Delta Pulse

[porkluvr]

evening porkluver,
poss also use a CD4098 , max 18V , recomended limit 16V , but still good.

same function and pin config as a 4538 but not classed as precision like the 4538, apparantly , funny , they still work well.

thought i'd chip in with another option.

Dooley, I thought you were right but I had to look that up.

According to the Intersil data sheet, CD4098 uses a different time delay formula (t=0.5RxCx, vs t=RxCx for CD4538 ). But, that means that we could double either the Rx or Cx value and then everything should be OK. (Double Cx and then use the same potentiometers as before.)

There are several other '4538' devices out there (such as MC14538, CD14538, HEF4538, HCF4538.)

These other devices have some minimum restriction on either the Rx or Cx value, or both. Some will work and some will not. For instance HCF4538 has a minimum Rx value of 4kΩ, with Cx minimum 5nF. (Ouch. I wish I knew that before I purchase 20 of them.) Don't try and use that here.
HEF4538 has a minimum Cx value of 2nF and also should not be used.

I believe the MC14538 and CD14538 are alright to use because they have no minimum restriction on Cx and their restriction on Rx is high enough that they can still be used on the DP.

My information may be erroneous - I am not setting myself up to be an authoritative source, that is what manufacturer's data sheets are for. My point is, anybody wanting to substitute one of the other parts would be wise to peruse the applicable data sheet before doing so. Don't assume anything.

[porkluvr]

Dooley, I thought you were right but I had to look that up.

I believe the MC14538 and CD14538 are alright to use because they have no minimum restriction on Cx and their restriction on Rx is high enough that they can still be used on the DP.

I misspoke. Referring to MC14538 and CD14538 timing resistor Rx:

"...although there is a restriction against using very low values of Rx, DP uses higher values of Rx so that it should not matter."

I think that makes more sense.

[szucs_g]

On right! Polyester are. :-)

Thank You for Your help! I think I replace my dealer because he says it always, that this it is can be substituted. Though not too right. It ne556 15 nF were not good instead of a capacitor the 22 nF, but it given, because 15 nF were not on a depository. :-)
Now from an Internet department store I ordered. As soon as I exchange it I write about the developments. Thanks.
Gábor

[szucs_g]

Good idea it, if something is we would create with a step-up converter a stable 13 or 14 volts and we would run it onto the instrument? There is booster that 3 V capable to 14 volts manufacture. Would DP work with this?
Hi! Gábor

[szucs_g]

It's true! The 74HCxxx working 3-6v and the CD series 3-16v or 18v. I see it now, that the CD4538 working with +E and -E. So the 74HC a series does not endure it really. Fortune, how was not smoking till now. :-)

[DOOLEY]

cheers porkluver ,

that explains why i had to nearly double the cx values to get the same timing pulses after i substituted a 4538 for a 4098 when i built a version of the blind squirrel.

they still works well ,but i found a site comparing the 4098 to the 4538 and it said "the 4098 is not as precise as the 4538"
i expected the worst with unstable / fluctuating timming , but no , all stable , happy with the 4098 , and there 1/2 the price.

[szucs_g]

CD4538 these are in the PD.
http://pdf1.alldatasheet.com/datashe...CF4538BEY.html
Theoretically -0,5 -18 volts it's working. The detector not yet indicates any metal.

[porkluvr]

HCF4538 is not one to use. Datasheet states that minimum timing capacitance is 5nF which is higher than the 1.5nF used on the DP. This is stated on page 2 of the datasheet.

CD4538 and HCF4538 are not equivalent. They perform the same function, but HCF4538 imposes constraints on timing components where CD4538 does not.

(Don't know for sure but this restriction on timing components may be due to HCF4538 having schmitt trigger inputs where CD4538 does not.)

[szucs_g]

The mistake is found. I trusted the salesman. Said it, that it LM357 like the 356 good. You were wrong. Unfortunately this component it was not accused by me till now. The Internet department store's components arrived, I put them into it, but the 356 I exchanged it as last one only. See a miracle. It's working. It is possible to experiment with the depth. A battery of mine was destroyed in an alley. R.I.P.
Thank you for your help!
Newer moral! Only your own eye believe!

[szucs_g]

Not "You were wrong." The salesman were wrong. Sorry.

[Jose]

Not "You were wrong." The salesman were wrong. Sorry.

Hello Szucs
For your information, DP works best with the LF357.
regards
Jose

[szucs_g]

OK. Maybe my LM357 was wrong...

[ossamaussama]

try this

to make delta pulse work with lower delay

need to reduce the effect of feedback network on delay sample

by inserting 50k

and the gain have to be reduced

so use pot 100 k instead of 20 k

to ensure stability

and use 300 hz instead of

100 hz


try it and its work

now it can detect small gold

http://www.geotech1.com/forums/attac...1&d=1322337584

[Jose]

This is my mod DP, to detect small objects.
To decrease the delay, change the value of "C4 =1 nf".
Remove or open collector T2 leg 5 of 4538
To reduce the gain, increasing the value of R6 1.5 K
Increasing the frequency to 600 Hz
Pulse width adjust TX 125 usec.
regards
Jose

[szucs_g]

"Remove or open collector T2 leg 5 of 4538"

Why?