Redesign Questions #3
Comments
|
Thanks for reaching out, it is really cool that you are building a reproduction of this display! I don't own a case with such a display. Is this a logic chip on the left hand side? The easiest way would be to use the MHzDisplayBlaster schematic and just use a new PCB layout that matches the dimensions and hole locations of your display. This would make sure that the circuit is correct and you would just have to worry about the routing of the wires. But if you have reverse engineered the circuit of the display it would be nice to build an exact replica too :D |
|
Actually yes! This schematic and PCB is just a redesign of the MHzDisplayBlaster, though I have really just started. I thought it would be much easier than trying to reverse engineer the original one. I was also curious about the logic chip on the original as well and thought it was a pretty complicated design for what it is. One of the segments of the first digit is broken on the original so I tried to see if I could fix it. There are a group of resistors underneath the display that you can only get to by removing the display entirely. After I removed it, I also learned that the display traces do not connect to the traces on the back on the PCB, and instead are connected to the pads next to the resistors underneath the display. So you have to melt solder down the pins and through the through-holes and hope that they make the right contact. Very strange design so I thought I would give a shot at rearranging the MHzDisplayBlaster instead. I already have made an original MHzDisplayBlaster as well, but found that it wouldn't quite work with my case. But I have been super excited that you have created this as an option in general. So in regards to my question above, the snapshot of the schematic is from your original 7 pin connector. I am going to make it into a 4 pin connector and separate power and ground to the 3 pin connector to the back to fit in the case like the original. But in the schematic you have TurboSwOn, TurboSwCM, and TurboSwOff. It might not be clear from my description or photos, but I am trying to figure out which on of those my turbo switch should connect to. I am sort of thinking TurboSwOff might be the most appropriate, but I thought I would try to get some more perspective of how those three pins relate to each other. Thanks! edit - here is a photo of the back side with the logic chip if you are curious
|
|
So in your case there are only 3 cables coming in to the display: 5V, Ground and Turbo. The turbo switch in the MHzDisplayBlaster's schematic is a 3-pin 2-way switch connecting TurboSwCM to either TurboSwON or TurboSwOff. To get the same functionality with a simple 2-pin on/off switch you would need a different schematic. There is a way to get it to work using a chip like the 7406 (as on your display) and one additional resistor, but I would need to know where the other pin of the Turbo switch is connected to. Is it 5V so when the turbo switch is pressed you get 5V on the white cable, and if it's not pressed you are getting 0V ? |
|
Ah ok this makes a lot more sense and why I was a bit confused. I opened the case up and did a little probing. It seems that when the turbo button is not engaged, it is sending 1.62v through the white Turbo wire. When the Turbo button is engaged, the white wire is reading 0v. I have also created a fork and committed my initial changes to branch Gecco if you ever feel like to taking a look. |
|
1.62V is a strange value. (i) Is this the voltage when the display is connected ? Could you measure it with the display disconnected? Nice, I will take a look at your branch. |
You totally nailed it. This is the voltage with the display connected and the LEDs are red. When measuring the white cable while it is disconnected it reads 0v with the Turbo button pressed and depressed. On the topic of red LEDs I was thinking of using this display instead of the green. |
|
Hmm I still don't understand how the white wire works. So the white wire should be connected to one pin of the power turbo button. Is the other pin of the turbo button connected to ground ? But if this is the case there should be some resistor in between otherwise you wouldn't be getting 1.62V. Regarding the LTD-6940 display, I think it is compatible. It is a common cathode 0.56" display and the pinout looks identical to the LTD-6440G that I used. |
|
Thanks for your patience while I figure this out. I pulled the LED / Button panel off of the case to see if I get a better look at what is going on. Here is a photo of the button from the inside. So I pulled the multimeter out to check continuity and this is what I figured out. White <--> Black -> Display Board When the button is pressed it is bridging White to Black / Ground and would simultaneously be bridging the Turbo Sw pins on the MB if it were present. How this relates to the function of the display I am not really sure because the display is configured as it was when I picked it up from a craigslist ad. It should have had a 386 / 486 in it originally, but the original owners had upgraded to a socket 7 Pentium at some point. Pressing the turbo switch currently does not change anything on the display. It would however be nice to have it functioning and at some point I will probably use it with your throttle blaster design. |
|
OK so white and blue connect to the motherboard to notify it that it should be in turbo mode and get shorted when you press the turbo button. Same for white and black, but these connect to the display. And you have already checked that black is ground. But if this is the case then you should not be getting 1.6V on the white cable when the turbo button is pressed, you should be getting 0V shouldn't you? This is what I am confused about. By the way the turbo switch should probably be a 2-way switch, meaning that the middle pin connects to either side depending on whether the switch is pressed or not, so you could use it with the current design as a backup plan. |
|
So the 1.6v is present on white when the turbo button is not pressed. So I guess this voltage is sort of floating when it is not connected to ground? I am not exactly sure why this is but I can try probing around a little more on the display board to see what is happening. Ok if I am understanding correctly, you are saying that the middle pin / black wire would connect to TurboSwCM but left off of ground, the white wire would connect to TurboSwOn, and the unpopulated pin would connect to TurboSwOff? The motherboard also has a LED pinset for the turbo LED, but in this configuration I guess it makes sense to also plug it directly into the MHzDisplayBlaster instead? |
|
As I am studying the schematic to adjust to this configuration I am thinking it will be best for me to ditch the original 3 pin connector and crimp my own dupont ends that match your original pin set instead. Dedicate a 2 pin connector for power, then a 3 pin to handle the turbo switch. This will make things less confusing and lesson the possibility of accidently sending 5v where it shouldn't go. |
|
We can keep the 3-pin connector, but we need to to change the schematic a bit. I think I understand your switch works, so let me work on your branch for a bit and I will get back to you. |
|
Ok sounds good! I made a few changes in an attempt to have a better arrangement that will fit the clearance on the back side of the PCB. Feel free to make any changes you think are appropriate. I will let a photo of the backside so you have an idea of what space is available for connectors in the back.
|
|
Also, I adjusted the display and the cut holes position to what I think should be accurate. I am not certain it will be perfect until I order a sample PCB and give it a try, but after double checking with the calipers I think it is correct. Right now the components all lean heavy to one side, but I am also trying to consider how the routing is going to work with this. I feel like it is already getting a little complicated. |
|
I am using a different version of kicad so I don't want to mess up your files. Here are the changes I made:
Please note that I have not checked the orientation of the 3-pin connector, so it may need to by flipped, depending on the footprint you are going to use. I am not super confident that it works correctly so if I were you I would try to make some prototype to check that everything works as expected.
|
|
Wow this looks great! I will study it over so I can understand how you went about designing this. It really simplifies the design as well. Feel free to create a new branch and commit your changes to there if you would like. So far I haven't had any issues switching between different kicad versions. Thank you again for your help with this. I have very much enjoyed this as a learning experience for designing PCBs. |
|
My version of kicad did not overwrite the existing files, it created new ones (attached). These should be placed in the The next step would be to assign footprints and update the layout. If you get stuck let me know. |
|
Great! I was able to copy in just the schematic file and was able to make the appropriate updates to the PCB. Here is what I have so far. For U2 I decided to go with an SOIC-14. If I understand correctly the right type of logic chip would be something like this? I might also go with a keyed 3-pin connector similar to the original so that the orientation is easier. I am also wondering if through hole resistors are considered the most ideal for these types of applications, or if it would be ok to also use SMD to save a little space? |
|
It looks great! I would use through-hole components for this project both for the chip and the resistors. It looks like there is enough room. As for the chip, I think any 74*04 should work, but yeah I would go for the DIP package not the surface-mount one if possible. |
|
Going to try and finish some things up with this soon. The routing seems a little intimating but I am also looking forward to giving it a try. I am hoping I can get a test board ordered soon! |
|
Alright, I finally had some time to focus on finishing this design up. This is what I currently have. I am getting a little more comfortable using KiCad now so I did a bit of cleanup and adjusted the layout a little. I played around with the routing a little, but also used an auto router to help out with some of the trickier parts. Not sure if the ground plane is correct or wise to do but I thought it might be nice to use. I think what confused me a little was making sure that the routing is correct between the 74LS04 and the resistors. I think it everything is correct but I wouldn't mind a second set of eyes to make sure it is correct. Otherwise, I think I am ready to fabricate a prototype board and hopefully I got everything in the first try. I double checked the measurements and alignment of things but it is hard to know if it will be perfect. Thanks again for your help! |
|
I removed the ground plane as I realized it wasn't doing much and was also impeding some of the back plane traces. |
|
It looks great! Just make sure the rules checker pass in both the schematic and the PCB layout. By the way why didn't you use a through-hole 7404 chip ? Most people prefer through-hole because they are easier to solder. Also there doesn't seem to be too much room between the LCD display and the left-hand side pins of the chip, so soldering it there may be a bit tricky. Hmm the groundplane looks too small. Did you use the fill-tool to fill both top and bottom copper layers with ground? They are usually a good idea to keep them because they could save the chip from static discharges. Another thing you could add is some tables or notes on how to program it. Have you shared the project so I can take a closer look? |
I will use the rule checker and double check! I will check into using a through hole again on the 7404, but I think when I tried the footprint was much larger both taller and wider that I was having a hard time finding a way to make it fit without bringing it to the other side of the board. Changing the position might be fine as well, but I wasn't sure how much it would affect the routing considering it already has a lot of traces crossing each other. I removed the ground plane, but I agree that it might be a good idea to keep for that very reason of the static discharge. I also experimented a little with bringing it all across the bottom layer, or at least including all of the area through J1 and J2 pins. In the photo posted earlier the ground plane is only on the bottom layer and is copper filled. I had to make a slight adjustment from then to make sure there was a clear trace from R2 that also is routed on the bottom layer. I think that I think I removed it because I wasn't totally confident I was doing it correctly or was needed. I will look into this again if you recommend it though! When I enabled the views for the silk screen and text that you originally had, it was a large mess because I hadn't been adjusting things so I just removed everything on those layers. After looking at it now, I totally regret removing some of the programming notes you already had on there already that would have been very useful. I will see if I can find a good way to move some of them back or recreate them! You can find everything here |
|
Ok I put a good amount of effort and I keep getting more comfortable and familiar with KiCad. I think I am getting close.
I think this layout will work a little better. I still couldn't fit the DIP 7404 on the board so I had to stick with the surface mount. I did however switch it to the back side of the board which should make it easier if it ever needs to be removed / gives clearance from the display. I also manually routed everything this time which I think was important. I was able to follow the schematics this time to make sure things like the resistors and 7404 was connected in the correct sequence. At least I think I did it correctly. It is overall a bit cleaner this way too. The trickiest part was my end routing when connecting the display which had a lot of crossing traces. But I was able to make use of vias so I think it is done correctly. I also did a full ground plan on both layers. Hopefully this looks a lot better, feel free to look it over to make sure I kept things in correct sequence. I will still probably put some graphic notes on there as well before I finalize and send out to fabrication. |
|
Sorry, I haven't had the time to take a proper look at the kicad files, it looks really nice though. One way to get the ground plane reach the middle is to carry it with a ground wire to the middle and add a couple of vias to help it get applied to both layers. By the way does the original display have a model number ? I don't see a model number in the photos, but there might be a similar one listed here: https://www.minuszerodegrees.net/led_speed_display/led_speed_display.htm |
|
Ok that is good to know about the ground planes, I will give that a try. The original display does not have a model number and is mysterious. Going through all the links on that list you sent me, the closes one it resembles is ST-6A. It is not exact, but has the most familiar design pattern and the jumpers make a similar configuration pattern. On that note, how difficult would it be to add a turbo LED header, and maybe even a trigger header for ThrottleBlaster switching? |
|
Alright, I have added the graphical notes back into the project and I feel like I am pretty much ready for fabrication. I would still consider adding pin header for turbo led as well as a switch header for throttle blaster, but that is just extra at this point. I still wouldn't mind a quick look over of the routing if you find some time as well. I feel pretty good about it, but also would rather fix anything before fabrication.
Also any other comments or suggestions are welcome! |
|
I just took a look at your repository. It looks great, other than an unconnected pin of the display (pin 4). Don't worry too much about the layout, as long as everything is connected, and the rules checker doesn't report errors, it should work just fine.
For a turbo led header you can get the output of label 2 (after the first set of NOT gates), add a larger resistor, like 1K (such that it doesn't use too much current that would otherwise go to the display), and connect the resistor to a 2-pin header. That would be the positive pin. The negative pin should be connected to ground.
Hmm, I am not sure what you mean by that. |
|
Oh wow I didn't even notice that missing connection on pin 4 of the display. Thank you for pointing that out! Ok that's is sort of what I had in mind for the turbo LED as well, but wasn't totally sure how I should implement that. I see you are confused about my thought for the ThrottleBlaster header because I am realizing it is a mode of the ThrottleBlaster that does not exist. I guess I had an idea in my mind of connecting it to the single button used in mode 2, but using a different mode that could set between two different throttle presets. Maybe even as simple as full throttle when not engaged, then have it throttle down to a specified speed when engaged. Or vise versa I guess since turning the turbo on usually slowed the computer down. But I will have to look at my case wiring because now that I think about it I think there are already dupont connectors from the turbo button that can already connect to turbo on the motherboard if it has it. I could probably connect this to the ThrottleBlaster instead. |
|
Ah that's a great idea. I don't think the Throttle Blaster supports such a simple single-turbo-value mode. Correct me if I'm wrong, but if I understand correctly you need something that works just like the turbo button (some slow frequency when OFF and full speed when ON) but using the Throttle Blaster instead of the computer's Turbo circuit ? |
Yes exactly! Though maybe it could be that the turbo button would select between two different presets that could be configured, though full speed could be one of those presets if you would like. Them maybe even have a long press disengage and engage the ThrottleBlaster entirely. Not sure if that is too complicated, but even just the switching between the two presets could be useful in this case. |
|
I am still trying to figure out the best placement on the PCB for this since the case has such a small opening for connectors on the back. But just want to verify that this is correct for the schematic of the turbo LED above.
I am trying to place it right after the 7404 but space is tight so I am not sure how practical this is going to be. |
|
I would place it right below the 3-pin header, there is seems to be enough space for a 2-pin header. |
I was thinking the same thing, though when doing so I was getting a new error on the ground pin of J3 about thermal connectivity on the pad when I brought the new header down there. It wasn't difficult to fix by added some more ground plane vias, then I decided to run a dedicated ground trace just to be sure it was enough. But it was a new type of error I needed to correct. I think this will work though. I am going to give it one more look over, and if things check out I will send this off to fabrication. Then I just have to hope that I have all my measurements correct for alignment while I wait. |
|
Here are a few suggestions:
|
|
Sorry for the delay on this! I had decided to place a production order as it is currently just to make sure I could test the placement of the cutouts and display before trying to make any finalized changes. It arrived today, and without soldering anything together yet it looks pretty good. I ordered extra components for everything so that I could build and test to make sure the routing and everything electronically works correctly. If it all is exact then great! But this way I have another chance to make a few little tweaks before commiting a final release and pushing it to the main repo. A couple of notes so far. You are correct that the silk screen was not high enough resolution to display the graphic, so I will need to find a place on the masking, probably on the backside to display that information. There is also some random silk screen text that I missed that is randomly above J2 that I missed. Otherwise, I am feeling quite happy with how the holes and alignment turned out so far. I think it is going to be exactly where I need it. Components should be arriving tomorrow so I can see if the overall design is correct. I will be in touch, probably over the weekend! |
|
Here is the update after building and testing! Overall, everything went very well. I was quite impressed with how well the alignment turned out for mounting and the display orientation with the front panel display. There are a couple of things need a bit of revision that didn't work as planned.
Otherwise, I am quite pleased with the results for this prototype and will start making any necessary changes for the next production run.
Note: I used an extra green display instead of the red for prototyping. I will be using red for the final build. |
|
It looks great!
I don't understand what you mean. By the way could you push the latest version to github? The latest commit I can see is from Oct 31 and does not include the Turbo LED circuit.
|
|
Thanks for taking a look! Can you double check the repo as all of my commits should be pushed.
I am not sure if the looping is relevant and I only see it on label 1 of the 7404. Meaning it goes from the 7404 to J1, then J1 connect label 1 to J2, but then label 1 connects back to the 7404. Label 3 also does something similar, but it does not connect through the 7404. After looking things over, I am also confused as to why the display doesn't show segments when set to either label 1 or 2 but does work with the Turbo LED. I will do some more testing on it tomorrow and probe around to see if I gather some more info on what is going on. I was thinking a 4 pin friction lock would work well on the Throttle Blaster for the molex power input, but if I remember correctly the routing might have been backwards which would have put 12v on the 5v or something. But maybe I am incorrect on that. |
|
Ah yes you are right, I was indeed looking at the latest version of Oct 17. Looping shouldn't be an issue. Could you measure the voltage at "1" and "2" ? If the segments don't work they should both be at 0V, but then how can the turbo led work, because it gets powered by "2".
Yes that would be ideal. I need to update the board at some point. |
|
So I did some probing and label 2 is also only getting around 3.7v after the 7404. I had thought that maybe the 1k resistor on R3 was also affecting this voltage somehow so I tried removing it from the circuit. This made no difference and is still around 3.7v, and maybe even dropped it slightly lower down to the 3.6v range. I am going to double check the datasheet for the 7404 and see if I can spot anything unusual about the routing. |
|
I think the 7404 I used has something to do with the problem as the routing does not seem correct with the package. Either that or I am confused about how the inverter functions. I will study this a little more and potentially create a new symbol based on the 7404 that I used so that it might be easier to visualize. I will be in touch on this, but let me know if you have any insight on this as well. |
|
So you are getting 3.7V on both "1" and "2" regardless of the position of the turbo switch? I think a 74HC04 series chip is CMOS based so it may give you a voltage closer to 5V. The inverter chip works as follows: the A pins are the inputs and the Y pins are the outputs. So if 1A is 0V, then 1Y is 5V and the reverse if 1A is 5V then 1Y is 0V. Same for all 1-6 pins. |
|
Turbo Disable - "1" = 3.9v, "2" = 0v So the hex inverter seems to be working correctly with switching, but the voltages are low or being drained somehow. I will double check the schematic and routing to make sure it all makes sense. But if the above diagram is correct, it doesn't seem to me that things were wired correctly.
For example where it is labeled Turbo and connected to the 1k resistor just after the input header, this seems it would correlate to pin 14 or VCC in on the 7404. So I am not positive that the schematic translated correctly to the pin layout. If I discover this is the case, I will see if I can figure out the right method to update the schematic and maybe even add a custom symbol for 7404 so that the pins can be displayed exactly. |
|
The circuit looks correct to me. The "Turbo" wire should be connected to pins 1,3,5 of the 7404. Green LEDs usually require a higher voltage to operate than red LEDs, so the 3.7V generated by your 7404 may not be enough. My guess is that if you replace the green led display with a red one it should work. If you need a green display you may need a different 7404 chip, I would recommend getting one from the HC series, as they are CMOS so they should output a voltage closer to 5V, and are widely available and very affordable. |
|
Ok cool! I am not really sure why I went with that specific 7404 to be honest. After looking around a little more I found some HC series like you mentioned that are much cheaper to purchase as well. I only grabbed a couple so not a huge deal, but for some reason I thought the one I selected was my only best option. Maybe I had search filtering incorrect. I will trust that it is wired correctly and just make the few adjustments that I mentioned and get another production on the way! |
I just put together my latest revision which had a few adjustments to the holes and LCD placement. Overall everything went very well, and the placement of everything is much better than before. This time I did use the red display in hopes that the voltages would be correct and the turbo button would function correctly. Unfortunately it is doing the same thing as the green display so I think the next thing to do is replace the 7404 and hope that is what is the culprit. I may decide to do some other slight revisions, but overall I think this is going to be a working version and I am happy with it. Thanks again for your help! |
|
I replaced the 7404 and the display now works as intended with the turbo switch! The only thing that is giving issues now is when I connect the turbo LED to the header it draws too much current and the display turbo segments dim to barely visible. When I have a moment I might make one last revision and add a mosfet that engages with the turbo button and connects the LED directly to 5v and ground. This way the turbo LED will not need to share current with the display current. I hope things are going well! |
|
Sorry for the late reply, that's great news! |
|
Ah ok. I switched it down to a 330ohm, but I think I have some 1k and maybe higher around too. I will give it a try! |
Hello! Thank you for all of your awesome contributions.
I am in the process of making some redesigns of the MhzDisplayBlaster to fit a particular baby AT case that I have. It is my first time working with KiCad with this extent and I figured it would be a good project to become more familiar with how to use it. I was hoping I could get some insight about a few things.
Here is a photo of the example display I am trying to redesign.
Everything is front based except for a 3 pin connector on the back that interfaces with the case for power and connection to the turbo button.
It seems the pinout is as follows
( IN ) -> Black Ground
( + ) -> Red 5v
( - ) -> White Turbo Button
This is what I have on the schematic so far.
I plan on reducing the 7 pin to a 4 pin and adding the 3 pin to the back similar to the original display. I am just unsure where to best connect the turbo button ( - ) wire for proper function.
I still have a long ways to go on the PCB design and I need to double check all of the position and spacing of things, but this is what I have put together so far. I am a little worried that the trace routing might be a little too busy with this layout so please let me know if you have any suggestions.
I appreciate all the help in advance!
The text was updated successfully, but these errors were encountered: