Building an ESR meter, some help and someone to check my PCB layout

[ben7]

Re: Building an ESR meter, some help and someone to check my PCB layout

Here is the board layout I will go with. I added a few pads to place a cap parallel to R12 and enlarged all the pads. All the traces are .032 and in place of just one jumper I ran 2 short jumpers to keep it neat and away from the IC (instead of running the trace between 6 & 7).

I will look to see if I have any 1N581x diodes, but this might be something I will have to substitute later, as well as finding a 50uA meter. I may try to find a smaller value variable resistor if I need to. I can play with the 10k resistor as well if needed. I am planning to use the transparency/iron on method to make the PCB, but may end up drawing it by hand if I need to. If I do draw it by hand I will mate a template for the tabs first by putting two layers of plastic tape on a printout of the PCB, then using sharpened brass tubing, make holes for the tabs and peel off the top as a template for the pads and then just draw the traces with sharpie and a ruler. Hope the transparency trick works because it will save a lot of time.

I will get the transparencies this afternoon. I think I can fit 12 on one sheet so I will be able to play with heat a little and practice before making the final.

I guess take plenty of pics and do a build on this thread as well for anyone interested in seeing the progress. Should go really quick once the PCB is etched.

Good job, I think it would be nice (if you can) to include the part numbers (C1, R2, etc...) on the picture too, so we can double-check it better.

[garry7263]

Re: Building an ESR meter, some help and someone to check my PCB layout

here is an image of the board with the names and locations

[ben7]

Re: Building an ESR meter, some help and someone to check my PCB layout

here is an image of the board with the names and locations

I think your layout looks good, just, don't trust me, I overlook things sometimes

BTW, what are the dimensions of the board? It looks a little cramped. What are the maximum allowable dimensions of the board for your meter? I can also give a go at designing a board layout too.

[mariushm]

Re: Building an ESR meter, some help and someone to check my PCB layout

Hmmm..

Some notes:

You leave a lot of empty space under the 7805 regulator. As you only draw a few mA, it won't heat up that much even with 9v input, so you could move the resistors under it. It's unlikely they'll heat from the 7805 enough to change their resistance significantly.

Otherwise, those resistors seem like ideal to be replaced with a bussed resistor array:

http://www.digikey.com/product-detai...1LF-ND/1089000

It's cheap (not including the shipping from Digikey) and saves you board space, it's SIP, it's spaced at 0.1" (2.54mm) so they can go almost parallel near the 16pin DIP.


Moving the resistors towards the top may allow you to turn the 16pin dip chip 90 degrees taking advantage of the empty space under LSP2 hole.

The new space you have above the R17 and C6 would give you some room to distance those pads a bit so that you'd have room for solder mask and to have nice round copper pads for each hole, without two holes getting their round surface mixed together.

[ben7]

Re: Building an ESR meter, some help and someone to check my PCB layout

Using SMD would help with the space too, it isn't THAT hard to solder 1206 resistors, that is the size that I use.

Edit-0: A better chip would be the 74HC7540. It is an octal inverting schmitt-trigger buffer chip; the inputs are on one side, and the outputs are on the other. Together with marishum's idea of a SIP resistor pack, you can save a decent amount of space! I think you could use the two extra inverting-schmitt buffers in the circuit without any decrease in performance also.

Edit-1: If you go with the chip above, then you can use this resistor array. (It is from mouser though, I am sure that there will be something similar on Digikey too)

Edit-2: You could also use an LM78L05 (5v 100mA) regulator, instead of the large LM7805 one.

[garry7263]

Re: Building an ESR meter, some help and someone to check my PCB layout

I have thought about using SMD because I would like to practice soldering them. I am going by a previous design and using what is available to me atm because I am trying to fix a Magnavox 50MF231D/37 that has problems. I plan on going through the board cap by cap and an ESR meter would save me considerable time and offer an alternative to just pulling and measuring capacitance or testing for short.

I did see mini 74HC14M in this surplus store and do have a local distributor for SMD components so I may opt for being able to put it in a smaller case at a later time. As for right now, the meter and the box will fit this with a little room to spare fitting it sideways on one end leaving room for the 9v and the back of the meter.

I have been trying to print out the board on my printer but unless I print black and white, I can not print without resizing the image. Which is driving me crazy. So I have changed it to a png and edited it. Going to try to resize it after lunch and see if I can get it. Having a solid black and white image will mean more toner on the transparency, which means better masking. Sure would be nice if my vinyl cutter was not ruined from being in storage. that would be the easiest method. As soon as I get the board etched I will post some pics of my progress.

[magistertc]

Re: Building an ESR meter, some help and someone to check my PCB layout

Oops, post # 18, that R11 should be 3K3 = 3300 ohms = 3.3K ........

[barry wilkins]

Re: Building an ESR meter, some help and someone to check my PCB layout

Hi as I said in my previous email ,made some component changes to get more gain out of the amplifier .
Also added a small 14volt bulb in series with the output of the Ic so help to cure the drifting problem, pinched this idea from the first instrument HP made the 200.
Barry Wilkins

[ben7]

Re: Building an ESR meter, some help and someone to check my PCB layout

Hi as I said in my previous email ,made some component changes to get more gain out of the amplifier .
Also added a small 14volt bulb in series with the output of the Ic so help to cure the drifting problem, pinched this idea from the first instrument HP made the 200.
Barry Wilkins

Does the lightbulb really work? I can see how it might compensate for temp differences, but does it really make any significant change?

Also, did you mean post, not email?

My computer actually just died, so I can't post any schematics or pcb layouts (I am typing this from my kindle fire)