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We are four electronic engineers working in a company, and we have a lab, I think we have a logistic issue with our components, this might be a basic study case:

  • We have few racks with resistors, capacitors, chips, transistors, diodes, connectors, LEDs, and so on.
  • We have projects all the time, and have plenty of boxes with unsorted components in low quantities, for each project.
  • We currently don't keep track of our stock.
  • When we have a need for components, we would just order or maybe take a look before order at Mouser, Digikey, Farnell etc...
  • BIG ISSUE ::: When we need to pass an order, it would take at least 1 week for administrative reasons.

We have arrived to the point where we need to know:

  • What is cheaper? Keep a big stock (keep track of it) or order components we need (constantly)?

Update: I will add that, we have recently bought several SMD resistor/capacitor kits, and this simplified our situation. If you have any other tips like this it would be great!

uint128_t
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Cristian Mardones
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  • Not sure about what is cheaper. But i am sure the moderators will closenthe topic. In their world cost doesn't matter or relate to electronics. –  Apr 08 '16 at 07:58
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    For the matter itself, you have to simulate both cases in excel. Taking into account risks of delays, etc. The global tendency is JIT, just in time: minimum stock, supplies arrive on time. –  Apr 08 '16 at 08:00
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    @GregoryKornblum there is nothing that's really electronics specific about supply logistics. – Passerby Apr 08 '16 at 08:03
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    I´ve got quite a decent stock of components built up over the years - by keeping track of my needs and making sure that I keep a stock of the components that I need the most - as well as a good selection of resistors and capacitors. So - first step is to do an inventory and assess your needs. Also, you need to think about what is more important - the cost of components, or your time. – F. Bloggs Apr 08 '16 at 08:04
  • @GregoryKornblum: There's not a simple set of moderators. Anyone with over 3000 points can vote to close or reopen a question. You're about half way to having that privelege. Right now, there are 192 users with enough points to close/reopen questions. – JRE Apr 08 '16 at 08:05
  • You see, i am not active enough to push it, and i think the guys that are active are just that. They mostly are active and aggressive, and arrogant. Like their rating means more than just forum activity. I am not like that and don't want anyone to be like that. –  Apr 08 '16 at 08:18
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    There are quite a few people who are too eager with the close button - but this is *not* a "where do I buy X" question, and I think most people would agree that cost is relevant. – pjc50 Apr 08 '16 at 08:29
  • @GregoryKornblum: A high points count can mean aggresive, but it can also mean "likes to help people find answers." I'm proud of my points, because it means someone thought I was helpful. – JRE Apr 08 '16 at 08:38
  • And why would you ever think it gives you right to be aggressive? A bunch of guys with high rating closed my topic last week. Why? What exactly do they know better than me? And they are coward enough to not even answer... –  Apr 08 '16 at 08:40
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    I ask this question in order to develop faster in my electronic lab... this is not a factory or marketing question.... im interested in other engineers tips to waste less time looking for components , or keeping track of stocks.... im not the only one to have this problem i think.... – Cristian Mardones Apr 08 '16 at 08:42
  • Am I aggresive? I will mercilessly vote to close questions that are clearly off topic or truly half-assed. I generally leave anything questionable open. I looked at your questions, and see one that I did vote to close. The way it was phrased made it sound like a shopping question - "I need part X for less than $1." If you meant to ask what alternatives there are for fiber optics, and asked which one is cheaper, then I would not have voted to close. I try to make my votes based on a surface reading of the question, and the one about fiber optics reads like a shopping question. – JRE Apr 08 '16 at 08:50
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    I would try to work on these "administrative reasons" that it takes a week to get stuff. Show them how much this policy is costing and maybe it can change? – Houston Fortney Apr 08 '16 at 10:07

5 Answers5

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I'm going to disagree with others. No, don't bother keeping track of inventory. You are doing this for engineering, not production, so knowing the exact number of parts on hand is a lot less valuable than the time wasted keeping the system up to date, and the inevitable busywork when someone doesn't. Engineers need to be able to grab a resistor without having to fill out a form, even after the fact.

However, you do need to keep parts on hand. See my answer here for how we do it. That picture is quite old, and our parts stock is probably 30% bigger now, but the system is the same.

Instead of tracking inventory, keep a clipboard or a list in a computer somewhere of items that you are running low on, or wish you had. Whenever new parts are ordered, include the items on the wish list.

When you do order parts, get a few more than you need and put them in your lab stock. Usually buy to the next higher price break. For example, it makes no sense to buy less than 100 0805 resistors at a time. If you need three of one IC, buy 10 or 20. This is how items get added to lab stock. Sometimes when you buy one item, you realize you may have a use for a similar item and get a few of those too.

It also helps to standardize of certain parts. For example, there are many many small signal bipolar transistors that can handle a few 10s of volts, 100s of mA, and are reasonably fast with decent gain. In the absence of special requirements, I use MMTB4401 and MMTB4403 for these. We buy those a few 100 at at time, depending on where the price breaks are. Many other transistors would do, but sticking to a small number of jellybean parts when it doesn't matter simplifies your lab stock and ultimately production inventory.

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Olin Lathrop
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  • That's mostly the way I do things. There is a difference between production parts (which have inventory) and development parts, (Which may or may not make their way into a product.) Some of my parts get sorted by kind... R's C's IC... But I have other parts boxes that are organized around one project, so all the development parts for that project are in one box. For the OP and 1 week delivery: the idea is to have more than one ball in the air, so there is always something to do while waiting for a board spin or parts order. – George Herold Apr 08 '16 at 12:57
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One thing to keep in mind when ordering parts to keep on stock is the work time of the engineers.
If your engineers have to spend an hour writing an order list that includes common parts, then over time that will cost you more than just keeping a bunch of those common parts on hand all the time.

For example, a reel of 5000 100K resistors costs around $12. If you spend that $12 one time, then your engineers won't have to spend time rooting them out of the catalog and putting them on an order list everytime you need one.

For common parts, we used to have a rack with reels, and an organizer with trays.
We'd cut a few hundred off the reel, and put them in the organizer. When you needed some parts, you took then out of the organizer. When it ran out, you refilled from the reel. When the reel ran out, you'd reorder while you use up the parts in the organizer.

What would generally happen was that the reel would land on somebody's desk until we had to order something else anyway, and the new reel would just be part of that order.

If somebody had a project that needed more than few of some (cheap) part, we'd just order a reel and be done with it. Working that way, we built up a collection of common parts for the things we worked on.

Simple, cheap, no inventory software needed.

More expensive parts we kept in a storage area with an inventory and management program. We had stuff in there that ran from low price but too bulky for the organizer (audio connectors and the like) to expensive ($1000 per piece, low numbers in stock, mostly because our work consisted of customizing those expensive items.)

JRE
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  • Step 1, take inventory now. Right now.

  • Step 2, keep inventory accurate and organized from now on.

  • Step 3, Reassess needs at some time in future after you have your inventory issue resolved.

You should have commonly used parts on hand. And if you don't keep track of what you have, then you shouldn't be running a lab/business. If the engineers won't bother to check for what you have on hand, and needlessly order, get new engineers that will.

Passerby
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    This seems to place the value of components over the value of time no matter what. I disagree and I keep only an R kit, a C kit (which I don't inventory) then I overnight everything else from digikey. If you ever have engineers counting resistors, you are wasting money. – Houston Fortney Apr 08 '16 at 09:59
  • @HoustonFortney you seem to think I mean that they need to count to the individual resistor... Im sure whomever checks your expenses would be up in arms about excessive overnight shipping charges too. – Passerby Apr 08 '16 at 10:02
  • @HoustonFortney a quick check of Digikey shows that the minimum overnight shipping cost is 80 bucks. You seem to value gloating over saving money. – Passerby Apr 08 '16 at 10:07
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    Hmm it only costs me 20... But even at 80 there would be some (not all) circumstances where that saves me enough time to justify it. – Houston Fortney Apr 08 '16 at 10:10
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    Engineers shouldn't spend their time counting parts. They also need to be able to grab a resistor, capacitor, opamp, etc, withoug filling out a form or having to update a inventory system. That would be counter-productive. – Olin Lathrop Apr 08 '16 at 11:28
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Compared to your time, and your market opportunity (or the loss of it), components cost nothing.

You need to keep a selection of leaded 1k, 10k 100ohm etc resistors, for debugging. You also need 100nF, 1uF etc ceramic capacitors for the same reason.

Keep track of your stock with an excel spreadsheet (or a database if you are feeling flash!) Although you have multiple projects, do not use a worksheet per project, use one monolithic worksheet, your projects will have many common components across them if you know what you're doing. Then you can sort columns by project, or by component parameters (so you can use them), or stock number (so your BOM system can use them), or quantity (to see what you need to reorder), or cost (to see where your capital is tied up in idle stock when the boss asks, or to see what you can cheaply order 1000 of), or monthly use (to see where your forward supply risks lie).

Order 1000 5x3 antistatic bags, and find suitable drawers that will fit them exactly (or the other way round). Keep components in stock number order, always.

You must have a store keeper. It doesn't matter whether it's 40% of one guy's time, or 10% of each of you, as long as you agree what it is, and keep doing it. I was the 'putting bags back into order, and refilling empty ones' guy at my last job. About once a week I'd spend 2 hours blitzing the drawers.

Take components out of the system spreadsheet first, then components. Search for cap value, voltage value, package, tolerance on the spreadsheet, then find the stock number, then pull the component. You then don't have to worry whether you sort components by project, or voltage, or resistance, or type. Data first then stock is also much more likely to spot a discrepancy between stock and record, than if you just grab a component from stock.

Keep a minimum of 10x components for every active project. You never know when you might need to resource a prototype quantity, or a sudden order.

Neil_UK
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DigiKey has lots of kits. Those have worked well for us. Because we were only a short walk away from production, I built a database of production parts and part numbers. Production's database worked backwards. You could find part numbers but not resister values for example because the values were in alpha fields that couldn't be sorted.

Robert Endl
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