Hi!!, problem solved, the xtime composer have connection problems with DBUS, for this reason xtime composer IDE can't see the messages from udev about the connection/disconnection of the startkit, details about how it was solved will be HERE posted by me with the user name Sodor, it's waiting to be approved by a moderator so it can be published tomorrow. Now I can continue with the power stage board (I almost finish it).
My laptop HDD failed, all the info about this project are on google drive so I simply replace the HDD and reinstall Linux, there is the problem, before the failure I have Ubuntu 18.04 LTS with the IDE for XMOS startkit board xTime Composer, all was working fine and the IDE can connect to the startkit without problems, until now....
My laptop is old, so I installed lubuntu, the problem: there is no USBFS support, because has been deprecated, so I must create rules file for udev in order to mount the board, that is covered in this XMOS document, but after creating the rules for udev on /etc/udev/rules.d/ disconnect and connect the board and doing a service reload to udev the IDE didn't see the XMOS startkit, using lsusb command I can verify detection of the board, I think that maybe the rules file have problems.
So I need to fix that in order to continue with the XMOS startkit board, may be this take some time due my work and my family and add that I'm not an expert in linux...
Searching on google I found this where the user [Bimpelrekkie] tips about voltage drop on vout of LM350K is due thermal protection, I admit I overstimated that and iniatially I reuse a intel CPU heatsink to mount the LM350K... without the cooling fan powered.... and without thermal grease.....
Well after powering the cooling fan and using thermal grease for CPU the problem of voltage drop on LM350K was solved (or at least diminished at deprecable levels). So this means that I can continue and finish the power stage board, I only need to solder connections of the second L298H needed for the third VCM.
For my ToDo list: Learn more about IC thermal managment.
Well I know this will happen, is normal and life will be boring without problems, also problems makes success more satisfying when it's achieved.
As I advance on the circuit I also do tests, the first test was with only one VCM connected to LM298HM, at that time I don't see any aparent problem, but when I did test with two VCM connected to L298HN I noticed a voltage drop on the ouputs of L298HN to both VCM from 4.5V to 3.23V, I also measured voltage drop at output of the variable power supply (LM350K based), this tell me that voltage drop was on variable power source, so I made a test connecting both VCM in parallel direct to P.S. output, test conditions was:
Vin = 19.1V
Vout = 5.11V (without load)
Vout' = 3.51V (with two VCM connected)
RL = 5 Ohms (both VCM are 10 Ohms connected on parallel)
IL = 0.690 A (measured)
If you see there is a voltage drop of 1.6V on Vout when load is connected to P.S. I need to check the datasheet to find what is wrong here (or if this is normal). Also there is a voltage drop too if I use only one VCM but is low enough to overlooked it on first tests, so if I connect three VCM then the voltage drop will be more than 1.6V (however I don't tested it).
I don't think this problem is thermal related because LM350K use a large heatsink and the changes on Vout are fast as the change of load. Well I will start here the analysis to find the possible problem, wish me success.
The last time I said that I changed my mind about power stage, this is why... I used 4 MOSFET D-PAK STD22NM20N, a spare perfboard from those that PCBway always give away and other basic components.
Then I realized that will be difficult to put a heat sink on this and surely I will need a heat sink for each bridge... but while I was thinking about it I remembered that I have some L298HN on my parts bin. Those IC can control up to two direct current motors on both directions each one, two of them can control three HDD actuator arm, at 15 pin each IC I can use prefboard without problems also the horizontal package ease the mount of a heat sink even if I can place both IC appropriately both can share the same heat sink.
First I build only the minimum to control one VCM from opto isolators to L298HN and do some test, and this is the result.
If you see I soldered two perfboards togheter, in the end the area was much smaller than having used H-Bridge option, Optocouplers are 6N137. At this point the circuit is incomplete and has this schematic:
OK first I need to say that I've been a little lazy on this schematic, I used images from the datasheet of both IC I trust it won't cause much problem... So the schematic in part isn't the implemented circuit, the L298HN on the schematic show the full bridge composed of amplifiers 3 and 4, the implemented circuit used 1 and 2, the only differences are on pin used on the L298HN to use the amplifiers 1 and 2 (inputs and ouputs) check the datasheet for more details, also there is no sensing resistor on implemented circuit.
I test the circuit with this conditions:
Optocouplers Vin 3.3V
Optocouplers Vcc 5V
L298HN power suppy Vs 7V
L298HN Logic supply Vss 5V
HDD VCM connected on output of amplifiers 1 and 2
Test went well, and the HDD actuator arm move on both direction as Vin was a logic high on one optocoupler and low on the other and viceversa.
I have to say that just before I start the circuit build I tested all the 6N137 optocouplers on a breadboard and six of seven work, six is the number that I need, I don't have more 6N137 I must be very carefully to not damage any.
Now why 7V for L298HN Vs? the reason is that as I stated on past logs I want to supply the VCM with 4.5V - 5V, so the datasheet for L298HN says this:
and this:
The LN298HN has it's dual H-bridge based on BJT, if I want Vl = 4.5V to 5V then I need to apply a Vs that by subtracting the Vce drop from on transistors susch that Vl will be on the range, then from datasheet Vcesat = 1.8V to 3.2 at 1A current, on my case are 450mA to 500mA, so with Vs = 7V then Vl = 5.2V to 3.8V if Vl is above or under the range of 4.5V to 5V then I simply adjust Vs.
With the first try (Vs = 7V) the measured Vl on the output with VCM connected gave me 4.5 Volts, it work even with Vs under the minimum, datasheet says Vsmin = Vih +2.5V and with Vih = 5V Vsmin = 7.5V... but it works excellent!!! Sorry there is no photo of this :¬(, now I can continue...
In the next update I will show the power stage circuit completed and tested (I hope).
The first option on mind was to build an H-bridge with N-channel MOSFETS (because I have a bunch of D-PAK STD22NM20N on my parts bin) for that I need to use a MOSFET driver that also have on my parts bin, one for each H-bridge, so three will be needed, each one of 20 pins a PCB was the best option for this, desinged on KiCAD and use PCBway.... that killed the idea... first I don't want to make a PCB for this, I want to use what I have on my house and parts bin, use prefboards??... the ones I have are too small... the second option was don't use the driver IC and drive the MOSFETs directly using opto isolators, but I will need two power supplies at different voltage levels, one for low side MOSFETS with at least more than 5Vcd to drive them and other at 9.5 to 10 volts for high side MOSFETS, the problem: I have only two power supplies, both are fixed voltage, one at 5 volts and the other have multiple fixed voltage levels, (3.3v, 2.5v, 1.8v, 1.2v and 19.1v)... the solution was a simple one: build a variable power supply based on one of LM350K from my parts bin and use the 19.1v for Vin needed.
On top the multiple fixed voltage power source on bottom the 5V fixed voltage PS.
These are the guts of my multiple fixed voltage PS, made with love, the PS sections from a motorola microwave ODU, hot glue and a hacksaw.
and this is my new humble variable PS based on LM350K
The next step was to make the H-Bridge with the D-PAK MOSFET, but then again another change of mind happened, this time was too late... but that history will be for the next log.
I have dissablembled 4 broken seagate HDD, retired the logic board and cover top, I noticed that not all HDD are the same model because not all have the same number of plates inside, I thought that all 4 disk would be the same model because all looks identilcal and none have its external labels.
Whatever looking the related circuitry of the VCM the coil connections are exposed to pins used to connect to logic board, so I use a multimeter and search for a low resistante value.
On these pins I have 10 Ohms value, I applied 5V and the actuator arm moved fast, reversed the polatrity and the actuator arm move to opposite direction, the same test on the other 3 HDD revealed that despite they are different models all use the same two pins and read 10 Ohms value.
Starting from here I think that a operating voltage of 4.5 to 5 Vcd for each VCM is good enough for this experiment.
Is needed to remove a little piece of metal near the VCM, is used to maintain the actuator arm on rest position when is not in use, this because it doesn't allow a free movement of the HDD arm because when the arm is on certain position the magnets atract it to rest position.
Using pliers I carefully remove the metal post...
Now the HDD actuator arm can move freely on his restricted range.
By using our website and services, you expressly agree to the placement of our performance, functionality, and advertising cookies.
Learn More
Omar
