Project Cost Estimates (And Why I Don't Provide Them)
© 2020 - Rod Elliott (ESP)

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I am regularly asked to provide an estimate for the cost of parts for projects.  Mostly, this is impossible, and as a matter of course I do not provide estimates.  The reasons are described here, as this (hopefully) saves me from having to give the same reply over and over again.  In many cases, the person enquiring doesn't even tell me where they live, but somehow I'm still expected to be able to give an estimate.  I can't and I won't.

All circuit diagrams published for projects are clear and easy to read, and it's easy to do a rough count of the number of opamps, resistors, capacitors, power semiconductors, pots and other parts required.  I provide detailed construction notes (not including chassis) and a BoM (bill of materials), and these are made available when you purchase the PCB.  I do not include manufacturer or supplier part numbers.  Maintaining a list of these would occupy all of my time, as they change regularly and there are hundreds of suppliers worldwide.

The main points are ...

1. Different suppliers worldwide have different pricing, and it's unrealistic to expect me to know the costs (even approximate) of various parts for every supplier throughout the world.
2. Constructors will often have their own ideas as to which opamp they prefer to use, and these can vary in price from less than AU$1 to AU$10 or more.
3. The cost of the passive parts (capacitors, resistors) is generally low, but I don't know the average cost where you live.  You can get this easily from your local supplier(s).
4. Most projects require a chassis or case, and these can vary in cost from a few dollars to a few hundred dollars.  I don't (and can't) know what you would like to use - only you know that.
5. Power supplies (including transformers) are needed, or you may have one already.  The cost of transformers is particularly variable, and you can only get the price from your supplier.

Mostly, you can get a rough idea of the cost of parts for a PCB by counting the number of opamps, and checking the price (of the ones you whish to use) with your supplier.  For resistors, count them (a rough count is all that's needed), and the same for capacitors.  Most resistors and caps of a particular style will cost roughly the same - for example your supplier may list 10µF 63V electros for $0.25 each, so simply count all electros, and use a 'guesstimate' of $0.50 each.  Resistors may list for $0.10 each, so multiply the total number by 0.1 to get a rough idea.  Some will need to be kept separate, especially wirewound types.

Potentiometers (pots) - both trimmers and chassis/ PCB mount types, are generally fairly inexpensive, and your normal supplier is the place to look.  Check their catalogue (whether on-line or hard-copy), and select the ones that match the suggested types shown in the project article.  In some cases you might not be able to get the exact same type (most projects with PCBs available show a photo of the finished board), but you will be able to get something similar - I avoid 'bespoke' or hard-to-get parts.

Power transistors (including MOSFETs) are usually the most expensive parts, and the cost of these must be obtained from your supplier.  Never buy expensive power transistors, opamps or other critical parts from any unknown supplier (such as AliExpress or eBay), because counterfeit devices are very common when the seller can be effectively anonymous.  Recognised major distributors may seem 'expensive', but they are almost always cheaper in the long run.

The above are the main points, but there can also be other costs, some of which are optional (and that I don't know).  For example, a project in the case of your choosing will need input and output connectors, a power switch, perhaps a heatsink (always needed for power amplifiers) and other features that you may want to include.  As noted already, cases/ chassis can vary from zero cost (you already have one) to hundreds of dollars.  This is always your choice, not mine.

Power supplies (and especially those for power amplifiers) are expensive.  The transformer is almost always the most costly, and the price for the rest depends on how much capacitance you want, the style of filter capacitors (some constructors will only use the most expensive caps available), and the way you mount everything - the chassis (again).

It should be fairly clear by now why estimates aren't provided.  There are so many variables that it's far beyond merely daunting, it's impossible.  However, by following the guidelines here you can produce your own rough guess far more easily that I can, because you know where you'll get your parts.

One of the difficulties of supplying to customers worldwide is the availability of parts.  I avoid (wherever possible) using anything that's only offered by a single supplier/ manufacturer, and in many projects I show alternative parts that can be used.  This is especially true for power transistors, and to a lesser extent for opamps, voltage regulators, etc.  There are a few where there isn't a choice, but the parts specified are available from most suppliers in almost any country you can name.

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