My first PCB

Markd77

Joined Sep 7, 2009
2,806
I just had a thought, it takes me a while sometimes. I could send you the displays and a PIC16F819, they could probably be with you by next weekend if you want.
 

Thread Starter

R!f@@

Joined Apr 2, 2009
9,734
I just had a thought, it takes me a while sometimes. I could send you the displays and a PIC16F819, they could probably be with you by next weekend if you want.
Thanks for the offer but I have to decline. :)
Like to learn and build.

I am learning cause this is just one of the few Voltmeters I have planned to make. I cannot expect you to send me all of 'em u know.

I have gone a bit far, the adapter is discarded Instead I made another layout.
Complete with PIC, Inverters and it's 5V reg. with all the components in a tiny SS PCB.

The RA0 part is yet to implement once I bread board to test it.
Eagle does not have a DIP PIC16F88, so I use a what is in the library. Pins are all the same.

The segment PCB layout is already done.

The connector which goes to segments is what I have. All I have right now is that IDC connector and cables.

All the components are from junk. So not necessary to comment on them.

Comments are welcome on trace layout.
The signals are routed under the chips and are 16 mil.
The Power traces are at 24 mil.
The jumpers are mostly used for Power.

I like to know whether signal routing method is OK.

I am using this method as I find easier to code. The inverters helps a lot.
I can use the same code later If I decide to buy CC 7 segs. Then I will omit the inverters in my next layout.

@ Mark
It's OK if you are bzy, I understand. I will tackle ur code with this board, It would be easier

By the way this layout too around 4 Hrs.
 

Attachments

Markd77

Joined Sep 7, 2009
2,806
I should have plenty of time to look at code tomorrow, some replacement parts for my bike arrived today so have mostly been fitting those instead.
You will still need 4 transistors for the common anodes of the displays. When an 8 is displayed they require 8*20mA = 160mA which I don't think inverters can deal with.
I meant to do it in code with compiler directives like this:
There's not too many parts which need changing.

If the #define line is commented out it compiles the second part instead of the first.

Rich (BB code):
;#DEFINE COMMONCATHODE

IFDEF COMMONCATHODE
;table is at start to avoid page crossing
bcdto7seg            ;bit 2 not used here (decimal point)
    addwf    PCL, F    ; Jump into the lookup table
    retlw    B'11101011'    ; Return segment code for 0
    retlw    B'00100001'    ; Return segment code for 1
    retlw    B'10111010'    ; Return segment code for 2
    retlw    B'10110011'    ; Return segment code for 3
    retlw    B'01110001'    ; Return segment code for 4
    retlw    B'11010011'    ; Return segment code for 5
    retlw    B'11011011'    ; Return segment code for 6
    retlw    B'10100001'    ; Return segment code for 7
    retlw    B'11111011'    ; Return segment code for 8
    retlw    B'11110011'    ; Return segment code for 9
    return
ELSE
bcdto7seg            ;bit 2 not used here (decimal point)
    addwf    PCL, F    ; Jump into the lookup table
    retlw    B'00010100'     ; Return segment code for 0
    retlw    B'11011110'     ; Return segment code for 1
    retlw    B'01000101'     ; Return segment code for 2
    retlw    B'01001100'     ; Return segment code for 3
    retlw    B'10001110'     ; Return segment code for 4
    retlw    B'00101100'     ; Return segment code for 5
    retlw    B'00100100'     ; Return segment code for 6
    retlw    B'01011110'     ; Return segment code for 7
    retlw    B'00000100'     ; Return segment code for 8
    retlw    B'00001100'     ; Return segment code for 9
    return



ENDIF
 

Markd77

Joined Sep 7, 2009
2,806
I think it looks pretty good with the inverters, not much more to do.
I presume the second digit decimal point just connects through a resistor to ground on the other board.
 

Thread Starter

R!f@@

Joined Apr 2, 2009
9,734
I presume the second digit decimal point just connects through a resistor to ground on the other board.
Yup.

Like to ask you how would be the RA0 input Voltage dividers that U used

What I found is attached.

Vout = (R2 / R1+R2) * Vin.

Will this method be fine.

My Voltage variation will be 0 to 40V.



{ed}

I did a bit of calculating.
I assigned a R2 value of 4.7KΩ.
Maximum RA0 voltage is limited to 5V, so at an input of 40V, R1 comes to 32.9K (33K).

I presume the Vout will now vary from 0V to 5V.

Any hints or advice on this is highly anticipated.
 

Attachments

Last edited:

Markd77

Joined Sep 7, 2009
2,806
I've stripped out the dead wood so it just needs converting to your PIC from the 16F819. It works fine on my setup, so should work with your inverters.
Just rename the attached to .asm and you should be in business.
For the voltage divider I'd put a high value variable resistor in parallel with one of the resistors and recalculate so with the variable resistor in the midpoint it gives 5V out.
You would have to be very lucky to get a 5V regulator which is exactly 5.000V and resistors which are spot on.
 

Attachments

t06afre

Joined May 11, 2009
5,934
Yup.

Like to ask you how would be the RA0 input Voltage dividers that U used

What I found is attached.

Vout = (R2 / R1+R2) * Vin.

Will this method be fine.
You must also take into consideration the RA0 input impedance. And as Mark said resistors are never spot on. Ad a port for fine tuning
 

Thread Starter

R!f@@

Joined Apr 2, 2009
9,734
Thanks a bunch.

I did exactly the same.
The Vin,s R1 has some parallel R & trimpot. I will use a trial & error and swap values until I get 5.00V at RA0.

I guess this is the Final Layout of both

{ed}
By the way, can I use the ICSP on the F88 so I can connect my Pickit3. I just have to connect straight to the ports without any thing in between, right ?
 

Attachments

Last edited:

Markd77

Joined Sep 7, 2009
2,806
Yes ICSP should be fine. The programming pins are connected to the inputs of inverters so there's no load on them. It works fine with my version too.
 

Thread Starter

R!f@@

Joined Apr 2, 2009
9,734
What would I do without you guys.

Hey I forgot to ask, would I need a cap like 100nF at the RA0 pin.

ICSP added. MCLR pin has to be a flex wire jumper :D
 

Attachments

Last edited:

tom66

Joined May 9, 2009
2,595
Are you etching the boards yourself?

Honestly I'd recommend getting PCBs made, you have so much more freedom. Seeed Studio do 5cmx5cm PCBs for $10 (a quantity of 10 are made for this price), plus $5 shipping, or $1.50 each. I use these guys often and can recommend them.
 
Last edited:

Markd77

Joined Sep 7, 2009
2,806
The capacitor might help, as might decreasing the values of both resistors if you can spare a few more mA. Recommended input impedence is <10K. I'm not sure how much difference it makes because my multimeter doesn't have enough resolution.
 

Thread Starter

R!f@@

Joined Apr 2, 2009
9,734
What do you mean by 10K. Is that the Total Z seen by RA0 should be <10K.
or the total of R1 + R2 should be <10K.

My Supply Amp capacity is 10A continues.
 

Markd77

Joined Sep 7, 2009
2,806
I'm not sure what it really means with a voltage divider, but apparently the reason is the leakage current of the ADC of +/-500nA. If you went down to 3K3 and 470R resistors that would definately be low enough, but they would have to be more than 1/4 watt.
 

Wendy

Joined Mar 24, 2008
22,145
Are you etching the boards yourself?

Honestly I'd recommend getting PCBs made, you have so much more freedom. Seeed Studio do 5cmx5cm PCBs for $10 (a quantity of 10 are made for this price), plus $5 shipping, or $1.50 each. I use these guys often and can recommend them.
I suspect he only wants one, which is why people DIY PCBs. Shipping to the Maldives is a lot more expensive than you credit, ask him how much 2 rolls of wax paper (worth $3.60) cost in import fees, not to mention shipping.
 

tom66

Joined May 9, 2009
2,595
I suspect he only wants one, which is why people DIY PCBs. Shipping to the Maldives is a lot more expensive than you credit, ask him how much 2 rolls of wax paper (worth $3.60) cost in import fees, not to mention shipping.
Yeah, that's the only disadvantage. Also, customs seems to take 2 weeks, plus the 1 week lead time for making the PCBs, that means it's 3 weeks+ to get your boards.
 

Thread Starter

R!f@@

Joined Apr 2, 2009
9,734
Ok Mark.

I changed the Divider to R1 (5K6), R2 (470R) & the Trimmer to 10K across R1.

This way I can adjust the RA0 Voltage ±2.5V or so around the 5V.
A jumper is added so I can disconnect the Pin befor adjustment.

The R1 (R19 is schema) is 0.5W per my calculation, R2 can be a SMD.

An ICSP header is added plus a 5V OK Led.

I like to ask how silk screen printing is done, what kind of paint is used and how it is transferred to the clad
 

Attachments

Top