DIY Digital Delay Generator Development Log - Page 1
Forum section: electronics / projects

author: mikeybarber
author_rank: Newbie
timestamp: December 29, 2017, 03:35:27 pm
content: I'm interested in developing a digital delay generator to sell online as a side business. I'm pretty sure that I won't be able to retire on something like this, but I wanted to document what it takes design & build a product and all the hoops that have to be jumped through to put a product like this up for sale on a site like Amazon, but for sure someplace like ebay.I didn't want to launch to crickets, so I thought I would document the process here and hopefully get marketing advice. In return to the community, I'll make everything available to build it yourself if you're interested, but I'm hoping that it would be cheaper to buy through me at the end of the day.I'm basing the design loosely on the user manual and specs for the Berkeley Nucleonics model 505. This model costs $2900 and has the following specs:- Qty 4 1-10V 50-ohm outputs. 2-20V un-terminated, 0.2nV/s slew rate- 10ns pulse width resolution- External trigger / gate- 0 - 2MHz internal trigger- Computer interfaces - RS232, GPIBI've attached pictures. Mine will look a bit different.Berkeley home page:http://www.berkeleynucleonics.com/model-505Direct data sheet link:http://www.berkeleynucleonics.com/sites/default/files/products/datasheets/505_ds_9-20-17.pdfI'm planning on using ethernet to interface to the box, & ditching RS-232 and GPIB.Since the delay resolution is 10ns, there will be no analog delays, only digital from an FPGA. I plan on using one of the new Max 10 CPLDs / FPGAs for this.I plan on using the LT1206 to drive the outputs, and vary the supply voltage to the amps, driving it in and out of saturation to get the 1-10V 50-ohm terminated outputs.For the ethernet interface, it doesn't need to transfer huge amounts of data, just SCPI type commands. I'm planning on using the ENC424J600T-I/PT from Microchip. Less than $4 from Digi-key.For power, I'm looking at the EPS-120-24 from Mean well / Mouser. Other rails will be obtained from switching / linear regulator circuits.Business Case:My sell price: $2kMaterial cost: $500Selling fees on Amazon: $235 (including FBA fees)Online advertising fees per unit: $100Profit: $1100 (roughly)I'm not sure how realistic the above numbers are, but this would be a rough profit of $10k per year at a qty of 10 units per year. Enough to be interesting as a side-hustle.Any feedback is appreciated. This is my first post, but this community seems pretty amazing.Thanks!

author: LaserSteve
author_rank: Super Contributor
timestamp: December 29, 2017, 04:01:23 pm
content: Hum, I used to work in an industry that used say 10-20 delay gens a year installing our systems at customer sites.If I went to my former boss and said lets use a off brand DG in a 50 to 350 thousand Dollar install, I would be asked what I'm smoking. Especially considering the market for DGs is one where the customer wants knobs and displays as they peak their experiment. Most users of DGs work in a situation where time is money and doing work where the needed precision is insane. Which means they will only buy from a reputable supplier.Its not a large market to begin with.Maybe for a little research college in Timbuktu Arkansas, but I don't think you have enough of a market unless you already have an electronics manufacturing business running to cover your hidden costs.In fact, we had a list of about 20 DGs we would not use, starting with DGs that had back terminated outputs. If a customer was using a DG on the "problem" list he or she would be advised to buy one not on the list before our installer got on site.You need a really good output stage with accurate programmable levels, variable offset, and awesome stability for this market.Steve

author: mikeybarber
author_rank: Newbie
timestamp: December 29, 2017, 04:21:35 pm
content: Steve - can you describe the industry that you worked in? What type of delay generators did you use? Many of the leading delay generators from Stanford Research or Berkeley have 1ps resolution from their analog delays. What kind of resolution did your equipment require?

author: LaserSteve
author_rank: Super Contributor
timestamp: December 29, 2017, 04:56:57 pm
content: Lab grade pulsed lasers.Telling you what I saw on site violates the NDA, but you can safely assume 1 nanosecond resolution, and I could not care a whit about exactly what that nanosecond was. What I did care about was repeatability and jitter, the quality of the trigger inputs, the sync output to the scope.For when interfacing to customer supplied interfaces, ttl is not always ttl, 5 volts is in the eye of the beholder, and 50 ohm inputs are rarely 50 ohms.Especially when dealing with mode locked lasers, your really concerned with walking the output pulse onto the targeted arrival time and keeping it there. Most such experiments are tuned with scopes, your A channel is the delay, and your B channel is the scope trigger. Often the C channel is turning something off.StevePlus the ability to save the settings.Steve

author: mikeybarber
author_rank: Newbie
timestamp: December 29, 2017, 05:30:48 pm
content: Is the external trigger to output pulse where you needed low jitter, or is it from the initial T0 timing edge output to the other output channels? The inter-channel output pulses usually have very low jitter with respect to each other.In terms of repeatability pulse to pulse, I've seen that most delay generators have the problem of external trigger to output edge being +/- one clock period of the fpga, or +/-10ns. You can get around this by syncing the fpga 100MHz clock to a reference clock input of 10MHz and using a PLL.If there is no clock to sync, ie it is some sort of environmental trigger, the only way to get low jitter is to use a time to digital converter on the external trigger input, then build this into the analog output delays. I'm not planning on doing that with this model.Most cases like your pulsed lasers though will use a trigger from something that has a reference clock, so you can get around this usually.

author: texaspyro
author_rank: Super Contributor
timestamp: December 29, 2017, 11:58:15 pm
content: Due to the issues mentioned by LaserSteve, you will have a tough time selling these for $2K. There are rather nice FPGA based digital delay generators out there with 10 ns res for under $100. Add a few bucks for hybrid digital/analog ones with sub ns res.One that I used (don't remember who made it) cost around $150. It used a digital signal to do the coarse adjustment from a 100 MHz clock and a digital delay line in the FPGA for the fine adjustment (I think it had 50 ps or so res). The fine delay had temperature compensation and calibration info in EEPROM). It could delay up to 2^32 coarse clocks.

author: LaserSteve
author_rank: Super Contributor
timestamp: December 30, 2017, 01:18:23 am
content: In my case Jitter is from external start signal to leading edge of "A" channel output pulse.Most scopes have horribly course sweep delay / trigger generators (if at all) so we always like to use one delay channel to pre-fire the scope sweep.Its rare in physics and materials science labs to find a nice clock to lock to. In some cases with ultrafast lasers yes, but rarely in other applications.The ability to trigger of rising or falling edges is desirable. The ability to invert an output is important as well.A trick used on some DG data sheets is to measure their performance before their internal back termination resistor. It also amazed me how many manufacturers tried to pretend the resistor was not there, and I'd see a half height pulse on the scope.When on the road I kept some BNC tees, a few 3dB attenuators, a 1:1,5 step up transformer, a few 50 ohm terminators and a couple of random lengths of cable in my tool kit to cope with DG issues.One thing to keep in mind, if you have never worked with Graduate students before, is the short circuit and overvoltage protection circuits you need on the inputs and outputs.One thing that surprised me, and we had many former Soviet block suppliers, is they like a small toroid transformer on their trigger inputs, which measured about 13 Ohms Impedance when I checked them in my home lab.. Hence my warning about input and output daffynitions.A typical application for us would be Channel A fires the laser pump flashlamp or pump diode pulser, Channel B fires the Q-switch 256 uSec after the lamp pulse, Channel C goes to the scope, and channel D might trigger the customer's data Acquisition. The 256 uS is the lifetime of the upper state of the laser material.In other cases we might do all of the above and run one customer event late, in other words lag one whole system cycle off the customer event trigger. In that case, one channel is the long delay and the other three run off its time out.In other cases the whole mess would run off our clock instead of the customer clock. It can go both ways with lasers.I've had some interesting conversations about what a leading edge is with many customers, some of which had a hard time understanding the 90/10 definition.Steve

author: LaserSteve
author_rank: Super Contributor
timestamp: December 30, 2017, 01:51:07 am
content: Quantum Composers is already selling what you propose for 1500$ on Ebay...My favorite slow DG , and one I'd copy in a FPGA , is the BNC 7010, its ancient, simple, but surprisingly useful. Much to former Boss's chagrin, I kept one from Ebay (75$) in the service car when not flying to sites. Chagrin, Till one day during one of those 300K installs, when the customer's new DG was dead out of the box. The factory engineer with me checked it using a 4 Ghz Lecroy scope and pronounced it very good. Install proceeded until FedEx showed up three days later. Time is money.Steve

author: mikeybarber
author_rank: Newbie
timestamp: December 30, 2017, 03:19:23 am
content: 1) The Quantum Composers box looks pretty nice. However, I personally don't like to have to run a PC to control a piece of equipment. Sometimes its nice, but it seems like the utility goes down if you can't turn it on a spin some dials. Also, I'm planning on offering adjustable amplitude outputs with up to 10V term / 20V unterm levels. You're right though - specs seem pretty close to what I'm proposing.2) The adjustable trigger input is a good data point. I'd like to have the user be able to switch between 1Meg / 50 ohm input term for the external trigger input, with adjustable voltage setpoint.3) The typical application you described seems to take advantage of the sub-nanosecond timing repeatability that can be achieved between the output channels.This is great information. Thanks for your detailed responses Steve.Mike

author: LaserSteve
author_rank: Super Contributor
timestamp: December 30, 2017, 05:39:43 pm
content: The fun one is, and this happens fairly often in the high energy physics world, is: Prime the DG, wait three, four, five hours to prep the shot, then hope the DG fires the sequence and the laser fires correctly. I had two customers that did that. The third one in that situation was smart enough to prefire the laser periodically. I'll let you guess why I mentioned that, but it might have something to do with liability disclaimers in the manual.I'd tell the story about the boss not calculating for coax cable velocity factor in one of those situations, but I may want to work in that industry again. Laser pulse arrived six inches too late, over sixty feet, resulting in customer tearing down their huge Marx Generator to move the b-dot sensor.My point being, mention Coax effects, and the usual Grad Student thing about using wire pairs on a BNC adapter in your manual. Often happens in the rush to graduate. Life would be better if they remembered to twist the pairs.Steve.