Author Topic: Bed of nail programmer - resources?  (Read 5297 times)

0 Members and 1 Guest are viewing this topic.

Offline jnzTopic starter

  • Frequent Contributor
  • **
  • Posts: 593
Bed of nail programmer - resources?
« on: January 12, 2019, 12:35:15 am »
I'm not sure, but I think there should be pogo pins that I can place into a 3D printed bed with some accuracy. Ideally I'd be able to find some pins that press in and I can run wires to, but I'm thinking it's more likely I'll have to roll a custom circuit board to hold pins and a 3D printed or machined fixture to then hold the board in the right place.

Has anyone made fairly inexpensive bed of nails programming fixtures and liked some parts or ideas over others?
 

Offline KL27x

  • Super Contributor
  • ***
  • Posts: 4108
  • Country: us
Re: Bed of nail programmer - resources?
« Reply #1 on: January 12, 2019, 12:52:43 am »
Are you probing random test points splayed out over distance to verify the board/circuit or are you just probing an ICSP/JTAG header?
 

Online langwadt

  • Super Contributor
  • ***
  • Posts: 4857
  • Country: dk
Re: Bed of nail programmer - resources?
« Reply #2 on: January 12, 2019, 01:30:37 am »
I'm not sure, but I think there should be pogo pins that I can place into a 3D printed bed with some accuracy. Ideally I'd be able to find some pins that press in and I can run wires to, but I'm thinking it's more likely I'll have to roll a custom circuit board to hold pins and a 3D printed or machined fixture to then hold the board in the right place.

Has anyone made fairly inexpensive bed of nails programming fixtures and liked some parts or ideas over others?

pcbs are so cheap it'll be hard to find something cheaper
 

Offline sleemanj

  • Super Contributor
  • ***
  • Posts: 3051
  • Country: nz
  • Professional tightwad.
    • The electronics hobby components I sell.
Re: Bed of nail programmer - resources?
« Reply #3 on: January 12, 2019, 01:54:09 am »
I recently (well, 6 months ago) made a pogo test jig, home etched and 3d printed. 



Don't underestimate the force required to press them down if you have a number of them, my jig has 30 pins, 15 a side it takes considerable force.  A toggle clamp ended up being the simplest way, I tried a number of different designs for a 3d-printed hold down method and couldn't get anything that was very reliable.

Even though the point of a pogo is that they can take up small variances, getting them aligned to the same height is still pretty important in my experience, they can be really finicky.

3d printing jigs - you'll probably go through a few designs, one problem I had is the very slight tolerance differences in my (admittedly old crusty and low quality) 3d printer meant that, for a 30 pin jig after tuning in in the hole diameter so it fit the pins snugly, some holes were too large and some were too small, so then you have to drill, which and getting the drill straight means a press really, and drilling PLA isn't great...

In all, next time I make a similar jig I would have perhaps been better to have printed a pattern on paper, glued it to wood and drilled that as the pin-aligning part of my jig underneath the PCB (or, indeed, attached the etched PCB to the block of wood and drilled both in a press at the same time).

~~~
EEVBlog Members - get yourself 10% discount off all my electronic components for sale just use the Buy Direct links and use Coupon Code "eevblog" during checkout.  Shipping from New Zealand, international orders welcome :-)
 

Offline cdev

  • Super Contributor
  • ***
  • !
  • Posts: 7350
  • Country: 00
Re: Bed of nail programmer - resources?
« Reply #4 on: January 12, 2019, 02:45:13 am »
I'm not sure, but I think there should be pogo pins that I can place into a 3D printed bed with some accuracy. Ideally I'd be able to find some pins that press in and I can run wires to, but I'm thinking it's more likely I'll have to roll a custom circuit board to hold pins and a 3D printed or machined fixture to then hold the board in the right place.

Has anyone made fairly inexpensive bed of nails programming fixtures and liked some parts or ideas over others?

The ones I've seen have used big thick pieces of acrylic plastic to hold the pogo pins, not 3D printed holders.
"What the large print giveth, the small print taketh away."
 

Offline jnzTopic starter

  • Frequent Contributor
  • **
  • Posts: 593
Re: Bed of nail programmer - resources?
« Reply #5 on: January 12, 2019, 04:17:09 am »
Are you probing random test points splayed out over distance to verify the board/circuit or are you just probing an ICSP/JTAG header?

A few JTAG pins, an a couple other points. Maybe 7 total.

Yea, that's the question is a machined ren or acryllic block the pins are pressed in, or a 3D print (we have an SLA machine, holds tighter tolerances than filament). I haven't looked to see if someone makes press-fit pins I think I'd need.
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 21611
  • Country: us
Re: Bed of nail programmer - resources?
« Reply #6 on: January 12, 2019, 04:30:58 am »
I helped build a test jig like that once. It used heavy fiberglass board about 1/6" thick with the pogo pins installed in it. The frame was made of wood with a cutout to locate the PCB and there was a hinge mounting the board that came down over the DUT.
 

Offline KL27x

  • Super Contributor
  • ***
  • Posts: 4108
  • Country: us
Re: Bed of nail programmer - resources?
« Reply #7 on: January 12, 2019, 05:56:16 am »
I've used a couple different kinds of pogo pins. The fancier one comes in two parts. The inner part is a complete unit, with contained spring and moving pin. The unit slides into the outer cylindrical housing, clicking into place. So they're replaceable.

The cheaper ones were a single part. So if the pin goes bad, you have to desolder w/e the pin connects to in order to replace it.

Ironically, the fancier pins are so well made, I have never worn out or damaged one of them. But it's still nice that you can change out individual pins and/or different spring forces and head shapes. The stiffer springs are quite stiff. You might need that to pierce through oxidation or flux residue. If working with clean ENIG pads, you can use the lowest force springs.

The cheap pins wore out fairly quickly, and they had more wiggle to them, radially.

Fancy pins:
https://www.mouser.com/datasheet/2/193/55-11775.pdf

They're rated for 0.05" center to center. I have never tried to solder them into a pcb like a thru hole part. The housings are about 0.034-0.038" in OD, per the datasheet. I imagine it is just possible with a custom pad shape. What I do is just solder the housings flat on their side to the pcb for a SIL 0.05" pitched interface. If you use two short rectangular pads on either end of the housing, you can flow and adjust one end at a time to straighten the pins and get them parallel. But it takes a steady hand, for sure.

Personally, I think the single point spear-head is the best for flat, clean pads. It has good piercing power and gives the most room for error in jig alignment. If you have any solder lumps on the pads, the multiple point serrated heads will register better on a lump in case of being slightly off but still have good piercing power. Rounded head pins are not that great on flat pads, IMO. I haven't found the point of them.         :-DD On the PCB I purchase, I can often see a single sharp divot where the test probes were placed, which I think is from a high force spear point.
« Last Edit: January 12, 2019, 06:31:19 am by KL27x »
 
The following users thanked this post: jnz

Offline jnzTopic starter

  • Frequent Contributor
  • **
  • Posts: 593
Re: Bed of nail programmer - resources?
« Reply #8 on: January 14, 2019, 05:10:57 pm »
I've used a couple different kinds of pogo pins. The fancier one comes in two parts. The inner part is a complete unit, with contained spring and moving pin. The unit slides into the outer cylindrical housing, clicking into place. So they're replaceable.

They're rated for 0.05" center to center. I have never tried to solder them into a pcb like a thru hole part. The housings are about 0.034-0.038" in OD, per the datasheet. I imagine it is just possible with a custom pad shape. What I do is just solder the housings flat on their side to the pcb for a SIL 0.05" pitched interface. If you use two short rectangular pads on either end of the housing, you can flow and adjust one end at a time to straighten the pins and get them parallel. But it takes a steady hand, for sure.

You don't happen to have a photo of the board you're mounting to do you? I think I need to see what you're talking about to really get it.
 

Offline KL27x

  • Super Contributor
  • ***
  • Posts: 4108
  • Country: us
Re: Bed of nail programmer - resources?
« Reply #9 on: January 14, 2019, 07:29:04 pm »
Umm, nothing to see, really. Just a row of pins soldered to a pcb. Then traced out to w/e you want to connect to it for programming or debugging.

[Imgur](
)
The one on the right is what I was describing. The pads are too short for these pin housings, because I used the same PCB layout as for the earlier models using the not-recommended cheapskate pins.

The one on the left is something that might interest you. I think the company is called TAG Connect. They make cables with a pogo pin interface on one end and a single row of female 0.1" header on the other end. I removed the pin cluster part out of the cable and attached it to a PCB. (The way the cable is, this part is enclosed in a small, rounded HDPE bead, so there's no good way to hold onto it or to attach it to a jig.) They use a DIL 0.05" pitch and the unique factor is the steel guide pins. This is really good for hand updating a long firmware in the field, or so I hear. But if you are using a jig of some type, it is not really needed.

[Imgur](
)
Here's another pic to show how the pins look outside of the housing.

They look fragile, but they are very sturdy. In the beginning, I built hard cases and always brought two when I had to leave the home office with them.  I also had bought plenty of backup pins. Nowadays, I still use some of these interfaces fairly frequently, but I couldn't even tell you where I put the spare pins. And if I have to drive across town with one, I just throw one in a side pocket of a laptop bag.
 

Offline IconicPCB

  • Super Contributor
  • ***
  • Posts: 1564
  • Country: au
Re: Bed of nail programmer - resources?
« Reply #10 on: January 14, 2019, 08:27:45 pm »
in order to achieve resonable pointing accuracy You need to use G10 base material which is at least 8 to 10 mm thick for the fixture base plate.
The probes do indeed come in two parts; a receptacle and the probe.
These assemblies ( receptacle and probe ) come in a range of sizes down to 0.025"diameter and even smaller.

The base plate is drilled using the prescribed drill size. Receptacles are then driven into the base plate flush with the top of the plate .Receptacles have a compression ring on their body whihc is used to hold the receptacle within the hole. A specific drift is neede to drive the receptacles into place.

This ensures pointing accuracy of the receptacle.
The probes also incorporate a number of features whihc ensure probe pointing accuracy and good electrical contact between probe sleeve and probe shaft.

The receptacle can have a crimp connection or wirewrap pin or soldercup for the wire.
Nothing majical just common sense.
And Yes I have sold and manufactured test fixtures.
 
The following users thanked this post: KL27x, jnz

Online langwadt

  • Super Contributor
  • ***
  • Posts: 4857
  • Country: dk
Re: Bed of nail programmer - resources?
« Reply #11 on: January 14, 2019, 10:00:12 pm »
in order to achieve resonable pointing accuracy You need to use G10 base material which is at least 8 to 10 mm thick for the fixture base plate.

I think stacking a number of PCBs could work, With the cheap protos you usually 5-10 identical PCBs anyway
 

Offline IconicPCB

  • Super Contributor
  • ***
  • Posts: 1564
  • Country: au
Re: Bed of nail programmer - resources?
« Reply #12 on: January 14, 2019, 10:17:10 pm »
Multiple bards would be a reasonable poor mans solution with reduced pointing accuracy.

You must keep in mind the probe receptacle is a sitting in a precisely drilled hole which will act on the compression ring of the receptacle.

That said 0.1" pitch probes will be quite tolerant of slight misalignments.

I am using the probes alone without the receptacles in a single  0.062" thick PCB specifically made for the task without any dificulty.
 

Offline cdev

  • Super Contributor
  • ***
  • !
  • Posts: 7350
  • Country: 00
Re: Bed of nail programmer - resources?
« Reply #13 on: January 14, 2019, 10:37:34 pm »
I've often wondered if there was some better way to build something like a temporary mini bed of nails, for holding contacts with some pressure onto multiple precise spots on a PCB.

Ive seen some solutions which are sold commercially. They're fairly pricey, most of them.
"What the large print giveth, the small print taketh away."
 

Online langwadt

  • Super Contributor
  • ***
  • Posts: 4857
  • Country: dk
Re: Bed of nail programmer - resources?
« Reply #14 on: January 14, 2019, 11:08:27 pm »
Multiple bards would be a reasonable poor mans solution with reduced pointing accuracy.

You must keep in mind the probe receptacle is a sitting in a precisely drilled hole which will act on the compression ring of the receptacle.

That said 0.1" pitch probes will be quite tolerant of slight misalignments.

I am using the probes alone without the receptacles in a single  0.062" thick PCB specifically made for the task without any dificulty.

making the pcb holes the minor diameter of the receptable, using the ring as a depth stop and stacking the pcbs far apart as possible
should make it at least as accurate as a pcb

 

Offline IconicPCB

  • Super Contributor
  • ***
  • Posts: 1564
  • Country: au
Re: Bed of nail programmer - resources?
« Reply #15 on: January 14, 2019, 11:25:27 pm »
If I didnt make it clear...
the receptacle is driven into the plate with a special drift ( tool to drive the receptacle correctly) .
The compression ring is  compressed inside the hole to retain the receptacle in place.
 

Offline IconicPCB

  • Super Contributor
  • ***
  • Posts: 1564
  • Country: au
Re: Bed of nail programmer - resources?
« Reply #16 on: January 14, 2019, 11:32:23 pm »
Cdev,

Yes there is. I used to run a subcontract bare board test laboratory. I had a universal grid single density machine with a cassette structure for its bed of nails function.

Spring loaded probes ( some 30,000 odd thousand ) were interposed between test electronics points and user accessible 0.1" pitch universal grid which carried job specific fixture built with rigid probes.

The spring probes were covered with a "striper" plate which exposed heads of spring loaded probes and engaged with the bottom plate of job specific fixture.

The only thing that changed in this kind of setup would be job specific fixture.
 
The following users thanked this post: cdev

Offline KL27x

  • Super Contributor
  • ***
  • Posts: 4108
  • Country: us
Re: Bed of nail programmer - resources?
« Reply #17 on: January 14, 2019, 11:38:38 pm »
Quote
That said 0.1" pitch probes will be quite tolerant of slight misalignments.
I have used my sidewards interface at 0.05" pitch in a CNC mill. PCB misalignment is the major factor in the deal. If you can't get the pins straight enough in thick FR-4/G10 block, I imagine you might try using a plastic like acetal or hdpe. There's no grain in the plastic and it makes for straighter drill holes. 
 

Online langwadt

  • Super Contributor
  • ***
  • Posts: 4857
  • Country: dk
Re: Bed of nail programmer - resources?
« Reply #18 on: January 14, 2019, 11:44:22 pm »
If I didnt make it clear...
the receptacle is driven into the plate with a special drift ( tool to drive the receptacle correctly) .
The compression ring is  compressed inside the hole to retain the receptacle in place.

I know that is the intended way, that doesn't mean you have to do like that

https://www.pjrc.com/teensy/beta/testfixture_nails1.jpg
 

Offline IconicPCB

  • Super Contributor
  • ***
  • Posts: 1564
  • Country: au
Re: Bed of nail programmer - resources?
« Reply #19 on: January 15, 2019, 03:58:28 am »
Langwadt,

So true. I have built a little programing fixture based on 6 pin AVR  pattern. Pins had some programing issues so i drilled a small second layer PCB to straighten out the pins and simply used super glue and bicarbonate of soda to hold it all together.

Bicarbonate of soda acts as an instant hardener of super glue.
 
The following users thanked this post: cdev


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf