Any tips to route this pcb ?

Discussion in 'The Projects Forum' started by André Ferrato, Apr 21, 2015.

  1. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    Hi, i am not being capable of routing this pcb using just the bottom layer, if anyone could have a look and give me some component positioning advice. I use 0.1uF for each IC, the 220Ω resistor is for two in series LED that will be attached with a 2 PIN connector. I'm trying to do it for a long time but with no sucesss :(.

    http://i.imgur.com/vF05QwR.jpg - ACTUAL diagram.
    https://www.virustotal.com/pt/file/...b93270035b6e776320862cf0/analysis/1429636526/ - 53 Antivirus scan of the attached file
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,974
    3,220
    I don't have the software to read those files.
    Post them in a standard graphics file format such as .gif or .pdf (not .jpeg)

    In general it may not be possible to route that circuit on one layer. That's why we have multi-layer boards.

    The best you can do is look at a rats-nest layout connection diagram of the circuit and then try to see how best to arrange the parts to minimize wire crossovers. Make sure you take advantage of running traces underneath through hole or surface mount components.
    But even after all that you may still have to use some wire jumpers (zero ohm resistors) for the few traces you can't route.
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    899
    I agree. Routing on one side without jumpers with that parts placement will be difficult. Can some of the devices be flipped? Which devices are positioned and cannot be changed? How many jumpers are you comfortable with?

    BTW, some members here will not open zip files as a matter of personal policy. The forum allows posting the sch and brd files directly.

    John
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    899
    I have been playing with it a little. The pads for your IC's seem quite large. It is usually easy to pass a wire between TH pins. Can you change to the oblong shape? Why do you need that group of 5 resistors in series?

    You will probably still end up with 2 jumpers. If you call them "zero" ohm resistors, they aren't so obvious.

    John
     
  5. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    Hello jpanhalt, i am confortable with anything that doesnt change the IC's i have. I enlarged every single pad because i'm going to manucfature this at my home in a PCB that has only one copper side, that is why it has just the bottom layer. About the resistors, i used 5 10k resistors in series because i needed 50k, and i have 5 of 10k at my home, but i can buy different ones. Everything can be repositioned and the vias need to a little large than the usual, usually 0.032 inch of width, for a easier etching process. Another thing i would like to ask, if the capacitors i'm using will do the job of smoothing the signal. The sch file is attached, i didnt manage to attach the brd file because the forum isnt allowing me to.

    UPDAE: I easily managed to route the board using top and bottom layer, but i only have the bottom layer at my disposal. Jpanhalt can you upload your version? With the jumpers so i can have a look? I thought about using air connections, but i wanted first to ask if any route genius can make this work without air connections.

    UPDATE 2: I thought about making two pcbs and air wiring them, the question now is how to handle this in eagle!
     
    Last edited: Apr 21, 2015
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    899
    OK, I have attached a board and schematic. Added two, zero ohm resistors. Ground is still not fixed. You can add some jumpers/zero ohm resistors or may find some easy routes I missed. I removed the instances in which I passed a conductor between IC pads. Hope I caught them all. Narrower pads really help avoid jumpers with pours.

    BTW: I thought both brd and sch files were allowed. Guess not. So, I attached a zip with both files too.

    John
     
  7. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    I saw what you did, really nice, i'll use the zero ohm resistors to represent the jumpers, it's a very good idea, thanks a lot jpanhalt. One last thing i would ask is: By looking at my design do you think i need to change something ? Like the 7.4v battery will hold ? The motors used are 3-6v 150mA max load, also the capacitors are good for this ? Another thing i worry about, the voltage drop at the battery when it's starts to discharge, the LM7805 needs at least 7v to drop it correctly to 5v, or it will start dropping 2v everytime, so a 6.5v battery would drop to 4.5v and that would affect the motors because there is already a drop at L293D because is transistor based. BUT i think for my project, a rf controlled car that needs to run for like maximum twenty minutes at a nice speed its good. Another thing, do you think is better to use those PCB's who are already drilled and i just make the vias or is better to etch a new one, or to spend more money in a breadboard ?
     
  8. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    899
    Whether the motors will drop the available battery voltage depends a lot on the battery, i.e., its internal resistance or current supply ability. 150mA max each for a stalled armature is not much. If that is running power, then starting current from a stalled condition will take much more current. You could consider an LDO regulator, and at his point, that change is easy to make. I would probably just switch to an LDO and worry a little less.

    As for making a PCB versus using various perf boards: PCB making can become a project in itself. Some people seem to make it a lifetime pursuit. If I were doing this for my very first project, I would focus on the outcome and use a perf board. There are different types of such board. Some are one sided, some have two sides with copper. Some have 3 holes per pad, others one hole per pad, and others have strips that run the whole length. And then there are combinations. The strip boards can give a very neat final product, but laying them out to give such nice results can take time. There are programs to help with that. One is called Fritzing. Three-holes per pad work well, but you may end up making more connections. Some people say essentially, you have make some jumpers so cut to the chase and use jumper everywhere. I personally prefer the strip style or the 3-hole per pad.

    Your new revisions were much improved aesthetically. Good work.

    John
     
  9. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    Understood, do you have a LDO in mind that reduces the 7.4v to 5v and be more secure for me ? I remade the board using jumpers, i'll upload so you can see the result. As you may note, i used jumpers between the encoder and the L293D and then one between the VCC's of the RF RX Module so i would need to connect the grounds and finally one for the data pins. I used a lot, is this a bad practice ? Also is it everything ? Can you check it for me.
     
  10. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    899
    One needs to know the current the LDO will provide before searching. There are a lot of available choices. One problem you will encounter is that as you go to very LDO, the devices tend to be surface mount. I recently made a small mobile deivce with the LP2989, which has drop-out voltages of 150 mV and 300 mV at 200 mA and 500 mA, respectively. But, it is surface mount.

    The LM1084 may work for you. Its drop out is 1.3V at 5A, and it comes in TH packages. Lots of options.

    John
     
  11. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    I took a look at this voltage regulator, it seens a good choice, but i dont havê any experience calculating the load that will come through the lm1084, so i dont know what resistors to use, could you give me a hand ?

    EDIT: Did you had a look at the board i uploaded ?
     
    Last edited: Apr 22, 2015
  12. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    899
    I looked at the board. That is a fair number of jumpers, also known as "bridges." The way you have accomplished that will work, but looks a little odd. Checkout the "jumper" library:
    upload_2015-4-22_18-3-39.png

    There you have nice bridges that work like variable length zero-ohm resistors.

    As for the regulator, all you need to do is make a good guess at the maximum current the circuitry in the receiver will draw. Values for the components are in the data sheets (i.e., HT12D, RF module, and L293). Add them up and be generous. From that, you can work out whether the LM1084 will work for you.

    I just noticed that you are using a switching jack for power but have tied the switched and unswitched outer ring contacts together. If you use Pin 2 for circuit ground, and Pin 3 for battery negative, then if you charge the battery in circuit, you won't be exposing the circuit to the charger voltage.

    John
     
  13. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    The problem is i get lost reading those datasheets, sometimes i dont know which value to work with it. I did not understand what you said about the DC Jack pins
     
  14. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    899
    On further reflection, I misunderstood your schematic. It was a last second thought that I didn't fully check out before posting. I was thinking, you were using the jack to charge an internal battery. In reality, it seems you are using it to plug in a battery or power supply. Forget my comment about using it as a switch.

    John
     
  15. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    Yes i'll be connecting the DC into 7.4v battery pack. I think will stay with the LM7805 for now. One last thing i ask of you, i know you saw my last thread about the transmitter, when looking into both the transmitter and the receiver do you think its going to work fine?
     
  16. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    899
    I don't recall enough about the transmitter to comment other than that both circuits are typical and should work. There may be problems with electronic noise, particularly from the motors. But seeing and dealing with that is part of learning from these projects.

    John
     
  17. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    Electronic noise? What do you mean
     
  18. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    899
    The motors are a source of noise. They produce spikes in the supply line (already discussed ). Sparking at the brushes produces RF. Capacitors across the motor leads or from each lead to the motor case and near the motor will help. The environment is also full of RF noise from other sources. You have some protection from RF noise with the encoding that is being used, but it will not be perfect.

    As I said earlier. That is a typical circuit. It has worked for many people. I suggested you focus on getting it working, perhaps using a breadboard or perf board to work out the unknowns before putting so much effort into a PCB.

    John
     
  19. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    I searched about the electronic noise you said. A solution i read about is to solder 3 0.1uF ceramic capacitors into the motor, two into the terminals and the case and one in parallel between the terminals. Another thing is to put more capacitors, like for the L293D that has 2 power pins, put one for each pin. One thing that i concern about what you say is the jumper wires, they will produce noise too ? Working like little antennas ? Also i use 0.1uF electrolytic for each pin, what is the difference between the ceramic and the electrolytic one ? When i should use one when i should use another ?
     
Loading...