New toy



  • I like the smell of lead too, although I use both :wink:
    My solder paste is lead-free.
    My Prop boards: P8XBlade2 , RamBlade , CpuBlade , TriBlade
    P1 Prop OS (also see Sphinx, PropDos, PropCmd, Spinix)
    P1: Tools (Index) , Emulators (Index) , ZiCog (Z80)
    P2: Tools & Code , Tricks & Traps
  • roglohrogloh Posts: 1,693
    edited 2019-01-06 - 12:23:56
    Hooked up a DC power supply to my board tonight and got some good initial results.

    Fed in 12V and got 4.99V out when driving a ~12 ohm resistive test load on the 5V output. Initial no load output was about 4.75V but was also still climbing slowly. Dropout for this regulator seemed to begin at about 6V so that should still suit 2 Li-ION batteries nicely.

    Efficiency appears rather good. The power supply's ammeter reads as 0.18A at 12V which means ~ 2.2W of power is being supplied under load, though I am not sure how accurate it's current meter is, and will need to check that. The 5V load is consuming 2.13W (actual load resistor was measured as 11.7 ohms), and this sinks 427mA. So the regulator's efficiency at this 427mA load comes out to be 96-97%. Tomorrow I will look at its output waveform and load it up more with a controllable current dummy load, but I am pretty happy to see this early result and my circuit/soldering effort doesn't seem to be DOA.

    Retested the load current with a more accurate meter, which is better than simply relying on measured load resistance. Am seeing 0.15A of power supply current drawn at 12V and 0.320A consumed at 5V by the total load (clip on cables/ammeter/resistor). This is 89% efficiency which is much more in line with the data sheet's numbers for the TPS563208.
  • Hi

    Flux pen- I've never seen one of those!
    Looked online- they seem to have a felt tip. The flux must be very liquid?
    Which can you recommend?

  • roglohrogloh Posts: 1,693
    edited 2019-01-06 - 11:58:39
    tritonium wrote: »

    Flux pen- I've never seen one of those!
    Looked online- they seem to have a felt tip. The flux must be very liquid?
    Which can you recommend?


    It's very watery and flows when you depress the tip. I have one, a decent Kester branded one #2331-ZX. Cleans up okay with alcohol. I've also used another Gel based one that is stickier (Chemtools NC254) but I don't like it as much, it's messier, though it does have a syringe tip for fine control.
  • roglohrogloh Posts: 1,693
    edited 2019-01-07 - 08:27:37
    Played about today with my board and tested the power regulator under controlled load conditions to get some better numbers. Here's a sample data point I looked at:

    Fed in 12.1V to the board from my power supply and measured 11.85VDC directly at the regulator's input, then using my most accurate ammeter I have access to here (1.5% error in its 6A range :frown: ), I measured 0.764A current being drawn from the power supply (the supply itself reported 0.78A).

    The output voltage from the regulator measured 4.97VDC at 1.62A with this same ammeter (after tweaking the supply voltage to maintain same regulator input 11.85V). So I think this is then ~89% efficient under these particular conditions.

    On the scope I'm seeing sharp switching spikes to about +90mV and - 150mV deviation from 5V under heavy load at the switcher's frequency but I think this should be able to drive the P2D2 regulators okay along with my other 5V devices on the board. Actual 5V rail noise stays within about 50mV or so from 5V at this load when I left persistence on for a while. I guess that seems reasonable for now and any actual dynamic load will probably change it anyway.

    Regulator and inductor get rather toasty and too hot to touch at much heavier loads, might need to measure that with Tubular later in the week to see exactly how hot.

    Update: using a thermocouple I'd found my multimeter came with, I measured the inductor temp and saw it measured almost 60C at this load above, while room ambient is about 25C. Seems a bit higher than what data sheet says for this load, though I didn't measure or compute the real inductor RMS current so I might be wrong there.

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  • roglohrogloh Posts: 1,693
    edited 2019-01-14 - 02:52:03
    Managed to find a few hours over the weekend to solder up a few more parts to my board and for trying out a couple of things.

    Got my (non Prop) USB micro-controller loaded and booting, and responding serially over USB to my Mac, echoing on a terminal app in a loopback condition and controlling the P2 RESET line using DTR. This now allows a prop-plug equivalent to be implemented on board using this micro controller's USART, that work has already been coded/proven on another experiment I did using the P1. The good thing is I can make the RESET pin's DTR behaviour be either active high or low or a low pulse on rising/falling transitions with very minor software changes. This micro-controller also controls battery charging/monitoring, some sleep/wake stuff and a few other things.

    To get this to work my 3.3V regulator circuit was also required to be installed and is now operational as well as the 5V power. I also tested the Rx/Tx and RESET pins right at the P2D2 socket and they are all active, so I think I am pretty much ready for loading in a P2D2 which I am patiently waiting for. Hope @Peter Jakacki gets it done soon otherwise this project sort of grinds to a halt once I've tested everything else. There are no more functioning P2D2's around Melbourne nowadays, and I missed out on the P2ES delivery too. So I have no P2! :frown: Still looking forward to Peter's progress.

    Also last week I visited Tubular and we measured the 5V regulator inductor temp via a FLIR camera. Under full 2A load this tiny 3mm square part was getting very hot (around ~105C or so), despite the fact that the thermocouple method I used earlier had measured much less than this (more like 60-70C). Even though the part is actually rated to 150C I don't like this temperature and will address that in my clean up spin by trying to add more copper around it for heatsinking and replacing with a larger and better spec'd power inductor with less than 1/4 of the internal DC resistance of the existing inductor. Increasing the copper heatsinking significantly is not that simple however as it is already a fairly tightly packed two layer board. So depending on the layout changes required I may also decide to split this 5V load current over two regulators with about 1A each instead of 2A on one single regulator, as half this load is optional anyway and I may not always need the 2nd regulator. I expect halving the current should drop the resistive loss heating in the inductor by something close to a factor of four (on each individual regulator) and make it more suitable for the enclosure. If I couple that with better inductors I think this heating issue should be resolved.

    In the meantime luckily there are no show stoppers and I can still make progress with the existing board for testing all the other things and finding any remaining issues.

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  • Nice going... you'll be needing a new p2d2v2 before long
  • roglohrogloh Posts: 1,693
    edited 2019-01-16 - 01:36:34
    Tubular wrote: »
    Nice going... you'll be needing a new p2d2v2 before long

    Yeah, actually I pretty much need one now... :lol:

    I have soldered up all the parts needed for a P2D2 to be powered and have code downloaded it into via USB serial. This first board currently has VGA, a USB host, USB serial slave, battery backed RTC, a 24 bit I2S DAC, and an SD card, plus plenty of IO expansion pins. I will probably also decide to add HDMI to this first board, instead of the usual Ethernet module (aka @Peter Jakacki's IOT5500, image attached). All connectors fit nicely inside the enclosure at the sides, so I didn't mess up the mechanical dimensions at least. Pretty happy with that. The HDMI connector may hopefully still fit through the case if required, but I'll just run this board standalone for testing HDMI. The thermal issue shouldn't be a problem on my first board when standalone without all the peripherals fitted as its regulator doesn't need to drive nearly as much current. So it should remain useable for my P2 experiments and further testing.

    I've found a couple of new PCB issues I can remedy in the next spin. The fuse component pad near the power connector was a bit too small for hand soldering as its SMD footprint was probably designed for oven soldering. I should really increase that in the board respin, but I think I managed to solder it down in the end (looks a bit ugly). Also I found one 3.3V net that was put down as a signal width track (6 mil) instead of a power net. It carries up to 400mA of current so I will want to increase that. Doh! Simply patched it up on this board with a small piece of copper wire bridging two capacitors and it's working ok.

    I will probably decide to make up a partial second board using this existing PCB layout to test my optional battery charger circuit stuff. That needs a couple of small pitch DFN SMD parts and that might be best done with the stencil I have, instead of risking hand soldering to this first board, though the pads do extend up the sides and I made extra long tracks to connect to it. There is also a QFN amplifier for driving some internal speakers, that one is going to be a real PITA. A wifi module can be added later too, the board can handle that.

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