Minipulse Plus Rev My time has come!

[mushaba]

Couldn't help my self waiting for components so I attached one of my 3dss coil...Just magical!!!Without setting the sensitivity trimmer the soda can is detected near 1m...Interesting though the particular coil that damped at 1.6k with the MPP with the CB it damped very nice and smooth at 560 Ohms with voltage near 440 volts..The preamp out is very clear so I'm thinking I have something faulty with my MPP pcb,I will have to look into the mur the mosfets and the preamp circuitry.I must notice that the CB has way more stable pulsing than the mine MPP..Difficulty is the pcb is both sides soldered and have small traces,take the parts out will need to be very careful,I wish I had another clear board...Never the less the CB seems to work very nice (even with 1 stage preamp)I adjusted the tx pulse at 150us and first sample at 10us(I can go lower).The frequency at 1000pps as advised,I wonder what is the sensitivity trimpot and how we should calibrate it.Also some directions I have at TP3 we calibrate for zero voltage at pr amp out,that done before the hole circuit is soldered,should I calibrate it again with the detector working?

I need your thoughts about damping guys especially George's advice since he is the designer..,what could be wrong with the MPP ...I'm thinking change the mosfets with a new one,the MUR diode and the 7555 pulse generator and the 5532.

[Qiaozhi]

Couldn't help my self waiting for components so I attached one of my 3dss coil...Just magical!!!Without setting the sensitivity trimmer the soda can is detected near 1m...Interesting though the particular coil that damped at 1.6k with the MPP with the CB it damped very nice and smooth at 560 Ohms with voltage near 440 volts..The preamp out is very clear so I'm thinking I have something faulty with my MPP pcb,I will have to look into the mur the mosfets and the preamp circuitry.I must notice that the CB has way more stable pulsing than the mine MPP..Difficulty is the pcb is both sides soldered and have small traces,take the parts out will need to be very careful,I wish I had another clear board...Never the less the CB seems to work very nice (even with 1 stage preamp)I adjusted the tx pulse at 150us and first sample at 10us(I can go lower).The frequency at 1000pps as advised,I wonder what is the sensitivity trimpot and how we should calibrate it.Also some directions I have at TP3 we calibrate for zero voltage at pr amp out,that done before the hole circuit is soldered,should I calibrate it again with the detector working?

I need your thoughts about damping guys especially George's advice since he is the designer..,what could be wrong with the MPP ...I'm thinking change the mosfets with a new one,the MUR diode and the 7555 pulse generator and the 5532.

The CB is a more complex design than the MPP, and is not considered to be a project for beginners. There are a number of improvements you could do to make it even better, such as swapping out the 7660A for an LT1054, which will allow you to remove the series diode that goes to V+. The diode is only there to protect the 7660A from getting too high an input from the battery pack when it's fully charged. Also, the preamp could be upgraded to have two stages (same as the MPP), and an MUR740 inserted between the MOSFET and the 3R3 series resistor.

It's difficult to know what's wrong with your MPP without probing it personally. Debugging remotely is always a difficult task.

[mushaba]

Thanks George for your reply,I will have all these advise in mind..I didn't ask for board debugging,just if there is any idea why the same coil dumps at different values in two Pi's running the same pulses with same components As I said above the CB won't go avalanche and damps nearly 560 Ohms so there is must be something faulty on my Mpp build.Nowhaving a second working detector I can spot clearly the difference in all points of pulse production and stages and won't go crazy������...Is there any advice on the sens trimmer and how to set it?

[Qiaozhi]

Thanks George for your reply,I will have all these advise in mind..I didn't ask for board debugging,just if there is any idea why the same coil dumps at different values in two Pi's running the same pulses with same components As I said above the CB won't go avalanche and damps nearly 560 Ohms so there is must be something faulty on my Mpp build.Nowhaving a second working detector I can spot clearly the difference in all points of pulse production and stages and won't go crazy������...Is there any advice on the sens trimmer and how to set it?

The MPP may be able to use a higher value damping resistor because of the 2-stage preamp and the series diode.
In my experience, I would set the sensitivity preset to mid position.

[mushaba]

...Also, the preamp could be upgraded to have two stages (same as the MPP

George here is a thought:IS it possible to modify the CB with 2 stage pre amp using NE5534 (i have a lot originals from TI and having trouble to order 5532 THT version) ??

Im thinking a small addon "card" ,the I/O of this card will be placed on the U5 (i hane installed an ic socket so i can change the opamp if needed) according to this schematic i made only based on how it is connected on the MPP.Dont know what values of R1 and R2 of this card and if i should change the values of R31-C13 and R25-V47 possibly...It should need 1 extra 0V from pcb.

[kt315]

NE5534/32 has protection diodes on inputs and you have to know that good before to use.
thats specific feature we discuss much times.

[mushaba]

NE5534/32 has protection diodes on inputs and you have to know that good before to use.
thats specific feature we discuss much times.

The first 2 diodes for first 5534 are on the CB pcb..Should I add 2 more?As I see from MPP preamp there are diodes only on first opamp input..

[Qiaozhi]

George here is a thought:IS it possible to modify the CB with 2 stage pre amp using NE5534 (i have a lot originals from TI and having trouble to order 5532 THT version) ??

Im thinking a small addon "card" ,the I/O of this card will be placed on the U5 (i hane installed an ic socket so i can change the opamp if needed) according to this schematic i made only based on how it is connected on the MPP.Dont know what values of R1 and R2 of this card and if i should change the values of R31-C13 and R25-V47 possibly...It should need 1 extra 0V from pcb.

[ATTACH]46423[/ATTACH]

You can use two 5532s in place of a single 5534, but each stage needs to have a gain of 33k. Look at the schematic for the MPP and copy that.

[godigit1]

I have a two stage plug in that was for the Hammerhead it will plug in pin for pin into the old socket but it is not for the 34.
its under plug in dual front end in the HH 1 thread.
Current gain is that of the HH 2.
Ive pluged it into a Surf pi and Barracuda It worked pretty good, The attachment cable I made could be better It could just be hard pinned into the socket .

[mushaba]

You can use two 5532s in place of a single 5534, but each stage needs to have a gain of 33k. Look at the schematic for the MPP and copy that.

Ok,lets break it down and please show mercy

At the MPP there is one NE5532 ic that contains 2 seperate amps.As i understand they are in connected as inverting amp the first stage and non inverting the second :
First stage (U2a) has a gain of: Gain=Rfeedback/Rinput --> Gain=R1/R8 --> Gain is 33.
Second stage (U2b) has a gain of: Gain=1+Rfeedback/Rinput --> Gain=1+R27/R26 --> Gain is 34.
What is the total gain of the 5532 on the MPP??


At the CB Gain=Rfeedback/Rinput --> Gain=R32/R8 --> Gain is 1000????

I have a two stage plug in that was for the Hammerhead it will plug in pin for pin into the old socket but it is not for the 34.
its under plug in dual front end in the HH 1 thread.
Current gain is that of the HH 2.
Ive pluged it into a Surf pi and Barracuda It worked pretty good, The attachment cable I made could be better It could just be hard pinned into the socket .

You say that you have a card like that for the HH but will not work for the 5534?For sure because they are different ic's.32 has 2 opamps inside and 34 has one,totally different pinout.

I asked George if i could implement this stage with the 5534 because i have 12 original TI ic's,i have trouble to source (from europe) 5532 in THT package.

Just dont know how much gain we need at the output

[Qiaozhi]

At the MPP there is one NE5532 ic that contains 2 seperate amps.As i understand they are in connected as inverting amp the first stage and non inverting the second :
First stage (U2a) has a gain of: Gain=Rfeedback/Rinput --> Gain=R1/R8 --> Gain is 33.
Second stage (U2b) has a gain of: Gain=1+Rfeedback/Rinput --> Gain=1+R27/R26 --> Gain is 34.

Correct.

What is the total gain of the 5532 on the MPP??

The gain is 33 * 34 = 1122

At the CB Gain=Rfeedback/Rinput --> Gain=R32/R8 --> Gain is 1000????

Yes, the gain is 1000, but it will work fine with 1122.

[mushaba]

OK!

Time for the stupid question (please excuse me but just a week ago i started studying about opamps):Our goal is to achieve specific gain or specific voltage at the output of the preamp??For example why did you stop at 1000 gain and you didnt go for 2000??I know that besides signal amplification we also amplify noise..

[godigit1]

. This is a add on board plugs in right where your 5534 goes and you can use a 5532 or max 412 or other dual amps with the same pinout.
My bad when I said it was not for a 534 its for a dual amp to replace a 5534. Will work on the CB.

[Qiaozhi]

OK!

Time for the stupid question (please excuse me but just a week ago i started studying about opamps):Our goal is to achieve specific gain or specific voltage at the output of the preamp??For example why did you stop at 1000 gain and you didnt go for 2000??I know that besides signal amplification we also amplify noise..

There are some simple designs that use a higher gain (such as 2000), but these are micro-based units with a 10-bit ADC. In this case, the higher gain is used to partially compensate for the lack of resolution. Depending on the opamp, you may be limited by the gain-bandwidth product. Also, the higher gain will force the opamp into saturation for longer, which means you need to sample later. As usual in any type of engineering, it's always about compromise.

[godigit1]

Wire your 5534s in this manner then you can use them as a double amp. but maybe you figured it out allready. Use your pin 4 and 8 for power and wire the amps dead bug style should fit right on your board.