Analog load cell amplifier IC for weighing machine with logarithmic output?

Hi -I want to make an electronic weighing machine with an analog meter display, NOT a digital readout.

Does anyone happen to know of a suitable chip? Load cells in one end, analog signal (ideally logarithmic) out the other end?
Thanks!

Hi.You can look at Cylewet CJMCU-711 HX711Cheers

Thank-you,  but I've looked at the HX711 already,  and it doesn't have an analog output.
(Btw, I only want to weigh up to say 1/2 a kilo.)

What sort of load cell are you using?  This impacts on the analogue processing needed. The application note on force sensors linked below covers a few of the commonly available types.Assuming it is strain gauge based what  are the specs on the load cell, if you are only weighing up to  500gm, then the load cell should be operating at a full scale value of 1-1.5Kgm, since the output in mV/V is at the full scale load.  What sort of stability do you need with time. Long term drift is likely to be a problem, and means of setting the zero  will be a necessity. There is a very good reason why precision sigma delta converters and  micros are used (particularly if you are not accustomed to doing precision analog electronics), its very straight forward to get good precision, stability,  an auto zero function, and a micro would do your log function and output it to a DAC.There are plenty of purely analogue load cell amps available from commercial suppliers of load cells. You would need to implement the logarithmic function yourself.If you want to roll your own, the all analogue approach uses an instrumentation amplifier, there is a lot of info from Texas Instruments and  app notes instrumentation amplifiers  and sensor conditioning  by Analog Devices  (the notes are old, but the same principles still apply)on how to choose and use amplifiers for load cells.The amplifier could be followed by a suitable logarithmic amplifier. Again, there is a lot of info on the web about designing these things. Your amp choice will be dictated by bandwidth, noise, drift, desired gain, power supply, headroom, to name a few of the obvious ones. A few more details would help,cheers,Richard

You could look at the TI XTR range. The XTR106  will drive a bridge like a strain gauge and provide a 4-20mA (analog) output. Conversion to a voltage is via a resistor (if you are unfamiliar with 4-20mA loops), although there is an offset for a zero input. Of course with some op amps,  you can get rid of the offset. It's a linear (as opposed to logarithmic) output I am afraid, but again, an op amp could make the conversion..

Hi and thanks.There's not really much to say about the application. I'm thinking of something like those little letter scales (amazing for the price!), but with an analog output that will drive a meter. It doesn't need to be terrifically accurate, but repeatable results would be good.I remember something about a simple diode having a good logarithmic response, and was thinking of trying to incorporate that somehow.I have some load cells (4 - yes, with the original wires) extracted from a digital kitchen scales. I was hoping to use those, and say half a dozen components plus the meter.It's just for testing and experimenting with, nothing fancy! I expected that the mechanical building would be the most tricky...

The load cell will be producing somewhere in the range of 1-5mV/V. If you work with a 5V supply, you will therefore get 25mV max. If the load cell is only working at 25% of full scale, then the signal will be around 6mV., and it could be as low as 1mV. To get the gain up to a few volts, you will therefore need a gain of at least 1000.  Log amps typically use dual op amps, although you can put diodes directly around a meter to make them non linear. The  log op amp route is well documented, and has the advantage that they can be made to work at low input voltages. You may be able to trade off some gain in the load cell amplifier with gain in an active log amp.This type of system will drift, it helps to use a stable reference to drive the load cell, this can be done directly from a medium current reference, since the load cells out of battery appliance are often up around 1K, rather than a few hundred Ohms. You will also need a pot in the system to zero it. You  probably won't be able to do an error budget since I guess you won't have the specs for the load cell.Just a few thoughts, hope it helps,cheers,Richard