Analog LIF neuron circuit and network of analog neurons - Page 1
Forum section: electronics / projects

author: Sariel
author_rank: Regular Contributor
timestamp: March 24, 2025, 07:01:56 am
content: I want to share a project I’ve been working on: an analog LIF (Leaky Integrate-and-Fire) neuron circuit.The circuit is shaped to resemble a biological neuron and mimics its behavior. It integrates incoming pulses with variable input weights, just like real neurons do.Right now, weights are adjusted using potentiometers. Later on, I plan to replace them with digital potentiometers for configurability.Once the membrane potential (represented by the voltage across a capacitor) crosses a certain threshold, the circuit fires an output pulse at the "axon tip" and rapidly discharges the capacitor, ready to accumulate again with new inputs.To visualize the behavior, I added a monitoring circuit with LEDs:As the capacitor charges, more red LEDs light up to indicate the increasing voltage.When a spike (output pulse) occurs, a green LED flashes.These neuron circuits can be chained together to form a fully analog artificial neural network (ANN). My next step is to introduce programmable interconnections, possibly using a device like the LMH6580 or a similar chip from Maxim.The design is inspired by a circuit I saw in Elektor Magazine by Clemens Valens.I’m attaching the schematic, and I’ve posted an awesome demo video on my LinkedIn.You don’t need a LinkedIn account to view it. If you run into any issues, let me know and I’ll upload it to my GitHub.https://www.linkedin.com/posts/sariel-hodisan_analog-neuron-circuits-work-and-beautifully-activity-7289620707716534274-ziyP?utm_source=share&utm_medium=member_desktop&rcm=ACoAAB3z4p4BAfCTj1xIFREKh87WExnM7qLL6vkSmall riddle:The monitoring circuit interacts in a negative way with the actual cell potential (voltage level). How and why?How did I solve it?

author: Sariel
author_rank: Regular Contributor
timestamp: March 24, 2025, 02:06:05 pm
content: I am adding some more information about the circuit behavior:The circuit features three inputs: two for integrating AC-coupled signals and one for connecting an inhibit signal that counteracts the integration and firing process. Additional inputs can be added in parallel to simulate more dendrites, expanding the circuit's capability.The AC-coupled input signals charge the integration capacitor (C3) through diode D1, which prevents the capacitor from discharging backward. A bootstrap circuit reflects the voltage across C3 back to the input, enabling charge accumulation with successive input pulses. Resistor R4, if included, provides the "leaky" behavior by allowing a gradual discharge of C3.When the voltage across C3 reaches a certain threshold, transistor T2 starts conducting, which raises the base voltage of T3. This causes T3 to conduct, rapidly discharging C3 to ground via resistor R2. During this process, T2 and T3 form a transistorized thyristor—a clever sub-circuit—that maintains conduction briefly.The conduction of T2 and T3 also activates T4 (a PNP transistor), which acts as a follower, driving the output to a low state. This low output is inverted by T5, producing a brief high-output spike.Once C3 is discharged, the emitter voltage of T2 drops, shutting off the transistorized thyristor. This halts conduction and stops the output, producing the short output spikes characteristic of this circuit.

author: xvr
author_rank: Frequent Contributor
timestamp: March 24, 2025, 06:31:00 pm
content: QuoteMaximum specified input voltage for LM339 is Vcc-2V (3V in your case). When memory capacitor charged to level more than 3V excessive current could be drawn by comparators inputs and discharge capacitor.

author: Sariel
author_rank: Regular Contributor
timestamp: March 24, 2025, 08:01:33 pm
content: Quote from: xvr on March 24, 2025, 06:31:00 pmThis is an answer in the right direction.The problem with the monitoring circuit starts even when the memory capacitor is still at 0V.